You're mixing up the need to follow God's commands with the need to be part of a covenant that requires following God's commands. Gentiles should not join the Old Covenant, but Gentiles should still obey God.
2 Timothy 3:15-17 and how from childhood you have been acquainted with the sacred writings, which are able to make you wise for salvation through faith in Christ Jesus. 16 All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, 17 that the man of God may be complete, equipped for every good work.
At the time Timothy was was a child, the NT had not been written, so the only Scriptures Paul could be referring to here is the OT. So the law is profitable for training us in righteousness and equipping us to do every good work. When 1 John 3:10 says that we should practice righteousness, that means to act in accordance with what the law instructs. When 1 Peter 1:13-16 says that we should have a holy conduct, we should again look to how the law defines that to understand how it means we should behave, starting with where verse 16 is quoting from.
1 Peter 2:8-9 But you are a chosen race, a royal priesthood, a holy nation, a people for his own possession, that you may proclaim the excellencies of him who called you out of darkness into his marvelous light. 10 Once you were not a people, but now you are God's people; once you had not received mercy, but now you have received mercy.
This is pretty much the same thing that God said to Israel in Deuteronomy, so Gentiles are being included as part of God's people and should act accordingly.
Again, there never was a requirement for all Gentiles to become circumcised, so that is in accordance with the law, not against it. There is a superior priesthood now, but Paul still continued to offer sacrifices, keep the Sabbath, the rest of God's Feasts, and we will also be keeping those things during the Millennial Reign.