Depends on what the Psalms express. If the Psalms are in line with the New Testament apostolic teachings, then yes. If no, then no.
Do ecumenical creeds, Christian Church since early times and the New Testament affirm the truth of everything in the Bible as Scripture? If so, then no part should be interpreted as contradicting another part.
Did the Apostates treat the Psalms as being an authoritative source? If so, then the Apostles should not be interpreted as expressing views that are contrary to what they considered to be an authoritative source and we should not considered them to be more authoritative than what they considered to be an authoritative source.
Depends on the specific case. I think it is clear also to you that plenty of the New Testament teaching is either independent on the Jewish Torah or even against it.
According to what God instructed in Deuteronomy 13, it is either incorrect to interpret the Apostles as speaking against obeying the Torah or they were false prophets, but either way followers of Christ should follow his example of obedience to the Torah.
Yes, this is why the orthodox churches do not keep Sabbath, for example. Christians are not lead by the Holy Spirit to do that.
God has commanded to keep the Sabbath holy (Exodus 20:8-11), so if you affirm that the Spirit has the role of leading us to obey what God has commanded, then part of that includes the Spirit leading us to keep the Sabbath holy. In Romans 8:4-7, Paul contrasted those who walk in the Spirit with those who have minds set on the flesh who are enemies of God who refuse to submit to the Law of God.
This is just your private interpretation. Anybody can say the opposite and who decides? The Church.
Do ecumenical creeds, Christian Church since early times and the New Testament ttake the position that God neglected to teach the Israelites what sin is? If not, then by what means did God teach the Israelites about sin is if not through the Torah? If God taught what sin is through the Torah, then the fact that Jesus was sinless means that he set a perfect example of how to walk in obedience it. Do ecumenical creeds, Christian Church since early times and the New Testament take the position that followers of Christ should follow his example of refraining from sin?
God is in the Church, not in the Old Testament commandments. God can make obsolete any previous commandment and He can make bounding any new one.
God's character traits are eternal, so any instructions that He has given for how to embody His character traits are eternally and cumulatively valid. For example, God's righteousness is eternal (Psalms 119:142), therefore all of God's righteous laws are eternal (Psalms 119:160), and if the way to embody God's righteousness were to ever change, then God's righteousness would not be eternal. For example, being a doer of charity was a way to embody God's righteousness before God made any covenants with man, so that is an eternally valid way to know God regardless of which covenant someone is under.