Questions/concerns:

Answers:

You began with stating that the ten commandments are still in effect.   You probably recognize that our agreeing on whether or not we should observe the Sabbath hinges on this statement.  Is it fact or a misunderstanding? 
 
I do not believe that we are presently under the ten commandments as the ten commandments.  I do believe that the new covenant under which I serve Jesus, includes all of the ten commandments except one, namely that servants of Christ in today's time should keep the Sabbath.  Let me also say that I believe the Jews under the law of Moses were to keep the Sabbath and also that the Jewish Christians in the writings of the New Testament kept the Sabbath.  You can show that the Sabbath was kept from Moses till and through out the period of New Testament writings.   I will agree with you on this.  You cannot show where, after Jesus died, that keeping the Sabbath was commanded.  I hope to show in the following discussion that, according to the scriptures, the Law and Prophets were completed and that they were not and are not the "perfect law of liberty" which Christians serve.   I use the New King James Version.
 
Jesus said in Matthew 5:17-18
 
Do not think that I came to destroy the Law or the Prophets. I did not come to destroy but to fulfill.   "For assuredly, I say to you, till heaven and earth pass away, one jot or one tittle will by no means pass from the law till all is fulfilled
You quote this same passage, yet you did not note that two conditions are required for the Law and Prophets to pass.  Heaven and earth passing away and all being fulfilled are the two stipulations stated by Jesus.
 
Heaven and earth passing is from another prophecy you quoted, Isaiah 66:22-23.  This passage does not say worship on the Sabbath but from "one Sabbath to another."  Actually the time was coming when the true worshippers were not bogged down with a certain day, but would worship continually. But lets discuss the heaven and earth passing way.  Jesus uses this passage as reference to the fulfilling of the Law, quoted above.  Jesus also uses the reference in Matthew 24:34-35.  Speaking of the destruction of Jerusalem, Jesus says:
Assuredly, I say to you, this generation will by no means pass away till all these things take place.  Heaven and earth will pass away, but My words will by no means pass away.
In this passage Jesus shows the fulfillment of the prophecy, it was to be in that generation.  Luke 21:20-22 further sets a time limit on the prophecies of the Jewish writings by stating plainly that: 
But when you see Jerusalem surrounded by armies, then know that its desolation is near.  Then let those who are in Judea flee to the mountains, let those who are in the midst of her depart, and let not those who are in the country enter her.  For these are the days of vengeance, that all things which are written may be fulfilled.
Luke goes on to say in verse 32, referring to these events that:
Assuredly, I say to you, this generation will by no means pass away till all things take place.
 Peter again references the prophecy to describe the anticipated time for which they waited.  II Peter 3:10--13 says:
  But the day of the Lord will come as a thief in the night, in which the heavens will pass away with a great noise, and the elements will melt with fervent heat; both the earth and the works that are in it will be burned up.  11  Therefore, since all these things will be dissolved, what manner of persons ought you to be in holy conduct and godliness,   looking for and hastening the coming of the day of God, because of which the heavens will be dissolved, being on fire, and the elements will melt with fervent heat?    Nevertheless we, according to His promise, look for new heavens and a new earth in which righteousness dwells.
Peter was writing to people of his day about what they expected.  The Jewish hope of a kingdom where righteousness would dwell is well known.  A key that has been overlooked in this passage is an understanding of the word "elements."  The Greek word from which this is translated is used five other times in scripture, Galatians 4:3, 4:9, Colossians 2:8, 2:20, and Hebrews 5:12.  Note them as follows.
 
Galatians 4:3-11 Shows that "elements" is not what we would think of in our modern world, but that it refers to concepts and ideas.  In this passage the reference is to elements of the Law.  They were released from this bondage as are all Christians.
  Even so we, when we were children, were in bondage under the elements of the world.  But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law,  to redeem those who were under the law, that we might receive the adoption as sons.  And because you are sons, God has sent forth the Spirit of His Son into your hearts, crying out, "Abba, Father!"  Therefore you are no longer a slave but a son, and if a son, then an heir of God through Christ.   But then, indeed, when you did not know God, you served those which by nature are not gods.  But now after you have known God, or rather are known by God, how is it that you turn again to the weak and beggarly elements, to which you desire again to be in bondage?   You observe days and months and seasons and years.  I am afraid for you, lest I have labored for you in vain.
Colossians 2:8&20
(8)  Beware lest anyone cheat you through philosophy and empty deceit, according to the tradition of men, according to the basic principles of the world, and not according to Christ.
(20)   Therefore, if you died with Christ from the basic principles of the world, why, as though living in the world, do you subject yourselves to regulations. . .?
Hebrews 5:12
For though by this time you ought to be teachers, you need someone to teach you again the first principles of the oracles of God; and you have come to need milk and not solid food.
From these passages we see that what was to pass away was not the physical universe but the elements of their law and government.  New heavens and new earth refers to a new order for a new dwelling place.  No longer after the destruction of Jerusalem would the kingdom of God be a location on earth.  It would be a new dwelling place, a new earth.  Revelation 21:1-2 says:
Now I saw a new heaven and a new earth, for the first heaven and the first earth had passed away. Also there was no more sea.  Then I, John, saw the holy city, New Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband.
This was after the destruction of the city "where also our Lord was crucified." - Revelation 11:8
 
It is with this understanding that we can understand Paul's teaching that the handwriting of requirements (ordinances) against the Colossians was "nailed to the cross" and his teaching in Ephesians 2:14-16
For He Himself is our peace, who has made both one, and has broken down the middle wall of separation,  having abolished in His flesh the enmity, that is, the law of commandments contained in ordinances, so as to create in Himself one new man from the two, thus making peace,  and that He might reconcile them both to God in one body through the cross, thereby putting to death the enmity.
The law was given to Israel and only Israel, Deuteronomy 5:1-2 and Exodus 19:3-6.  The Jews separated themselves from the Gentiles.  Until Christ there was a barrier. When Jesus came with a New Covenant sealed by his blood he brought the power to unite Jews and Gentiles.  It is in this covenant that all the blessings of being in Christ come.  We are no longer under the Law, if we serve Jesus.  It was his coming in judgment against Jerusalem that made the final and complete separation.  He promised he would come in that generation, Matthew 24 and other passages.  I believe that he did as he promised and that this fulfilled the Law and Prophets.  How about you?  Do you believe Jesus?
 
You also mentioned some passages in Romans.  I will deal with each one of them.  Please remember that as I understand the scriptures, the Law was still observable until the destruction of Jerusalem.  In fact James says that thousands (myriads) of Jewish believers in  Jerusalem were zealous for the Law - Acts 21:20.  Romans was written during the transition time.  But be that as it may, let's consider the passages.
 
Romans 3:31 "we establish the law" -- We cannot exclude this passage from the other passages in Romans 3.  Note verses 19-21.
Now we know that whatever the law says, it says to those who are under the law, that every mouth may be stopped, and all the world may become guilty before God.  Therefore by the deeds of the law no flesh will be justified in His sight, for by the law is the knowledge of sin.  21  But now the righteousness of God apart from the law is revealed, being witnessed by the Law and the Prophets.
The establishing of the Law through faith shows that the Law accomplished what God had intended.  All the world was guilty, the Jews who had the Law and the Gentiles who didn't.  This passages says nothing about the Law continuing.  In fact Paul says, as quoted, the righteousness of God is revealed apart from the Law. 
 
Romans 7:12 "The Law is holy."  The word "is" is added by the translators in verse 12.   If the translators are correct, the present tense of this passage clearly states that the law was in existence at that time. The present tense "is" is found in verse 14 which you also quote showing the Law to be spiritual.  If it was in existence, and I believe it was, then it was also holy and spiritual; it was from God.  But remember, it was being fulfilled.  Any Jew who believed Moses and the prophets (Luke 16:29-31) would also believe in Christ and would no longer need the Law.   In the opening verses of this passage we once again see that the Christian was separated from the Law.  Verse 4 says:
Therefore, my brethren, you also have become dead to the law through the body of Christ, that you may be married to another-- to Him who was raised from the dead, that we should bear fruit to God.
Note that the Christian became dead to the Law, not that the Law was dead to the Christian.  All of these passages show that while the Law might still have been in place and observable, it was not for those who served Christ.
 
Romans 7:22-8:1 is in the same context as the above.  Paul speaks as a Jew of the contrast between sin and the Law.   It is in this context that he says, "With my mind I serve the Law of God."  Verses 3 and 4 of chapter 8 say:
  For what the law could not do in that it was weak through the flesh, God did by sending His own Son in the likeness of sinful flesh, on account of sin: He condemned sin in the flesh,  that the righteous requirement of the law might be fulfilled in us who do not walk according to the flesh but according to the Spirit.
The righteous requirement of the law was fulfilled by Paul and others who walked according to the Spirit.  Until Christ, the followers of the Law had only the hope of death.  They always sinned, even good men sinned. Abraham, David, Isaac and all the others sinned for Paul says "all have sinned," Romans 3:23.  It was only when the obedience was taken out of the physical realm and put into the spiritual realm, that of Christ, that salvation was possible.   Consider the following questions a Jew might ask himself.  Did I ever fail to offer an offering? Did I ever fail to pay the yearly tax?  Did I ever lust after my neighbor's wife? Did I ever steal anything?  Most of these questions would be answered yes, I am guilty.  What was the solution the Law?  No the solution was, is and will always be Jesus.  The Law showed their guilt and that they needed Christ.  It was thus established and fulfilled.
 
Romans 14:5-6  "observes the day unto the Lord or does not observe the day to the Lord"  - Consider that in the church in Rome their were Jews and Gentiles.  The Law being still in place was observable and the Jews observed the various days and events.  As Christians, they did not offer sacrifices for sin, but the other observances were considered to be appropriate as Jews.  After the destruction of Jerusalem, they could no longer face the temple to pray.  They could no longer offer free will offerings.  After that destruction, there was no Law to observe, it was completed, fulfilled and finished.  Christ blood had made it unnecessary and useless.
 
Just a few more thoughts on the worship of Christians.  As Christians they worshipped on the first day.  As Jews they went to the synagogue.  The visits to the synagogue were to teach.  They may have worshipped also on the Sabbath, but in the New Testament, they also met for worship as Christians on the first day of the week.   What day was Christ raised?  - the first day of the week.  What day was the first Gospel sermon preached? - the first day of the week.  What day did the Church at Troas meet for worship?  Paul waited 7 days for -- the first day of the week.  What day did the Corinthians take up an offering? - the first day of the week.