The definition that I used is the only one that the NAS Greek Lexicon listed being specifically in regard to the context of fulfilling the law, it fits with what Jesus immediately proceeded to do next after he said he came to fulfill the law, it fits with how other verses like Galatians 5:14, Galatians 6:2, and Romans 15:18-19 use the term, it fits with how other Jewish writings use the term, it fits with the concept of someone fulfilling their marriage vows by correctly doing what they vowed to do, and it even fits with the definitions #1-3 that you listed.
On the other hand, definition #4 is contrary to Jesus saying that he came not to abolish the law, it is contrary to Jesus warning against relaxing the least part of the law or teaching others to do that, it is contrary to what Jesus proceeded to do next after he said that he came to fulfill the law as well, it is contrary to what Jesus taught by word and by example throughout the rest of his ministry, it is contrary to how other verses like Galatians 5:14, Galatians 6:2, and Romans 15:18-19 use the term, it is contrary to verses like Romans 3:31, which says that our faith does not abolish God's law, but rather it upholds it and Psalms 119:160, which says that all of God's righteous laws are eternal, it is contrary to how other Jewish writings use the term, and there is nothing else in the Bible that says anything along the lines that fulfilling the Mosaic Law causes the Mosaic Covenant to end.
So you'll need to provide good reason for rejecting the definition I listed in favor of using #4.
Jesus said that not the least part would disappear from the law until heaven disappear and all is accomplished, neither of which has happened yet, both of which refer to end times (Revelation 22:1) or are ways of saying that it is never going to happen.
The Bible often uses the same terms to describe aspects of the nature of God as it does to describe aspects of the nature of God's law, such as with it being holy, righteous, and good (Romans 7:12), or with justice, mercy, and faithfulness being weightier matters of the law (Matthew 23:23), and this is because it is God's instructions for how to testify about those aspects of God's nature. For example, our good works testify about God's goodness, which is why they give glory to Him (Matthew 5:16), and by testifying about God's goodness, we are expressing the belief that God is good, or in other words, we are believing in Him. The only way that eternal instructions for how to testify about God's eternal goodness can be ended is if God is no longer eternally good, and the same is true of other aspects of God's nature.
So the set of laws that the God of Israel has given paint is a picture of His nature and serve as an identity marker. For example, if the God of Israel had instead commanded His people to commit adultery, then that would paint a very different picture of His nature and someone who followed a God who commanded that would not be following a God with the same identity as the God of Israel. So if the New Covenant were made with a different set of laws that the Mosaic Law, then it would be made with a different God with a different nature than that of the God of Israel, but it in reality it is made with the same God with the same nature and therefore the same Mosaic Law for how to testify about His nature (Jeremiah 31:33). In 1 Peter 1:16, we are instructed to be holy for God is holy, which is a quote from Leviticus where God was giving instructions for how to do that, which includes keeping His Sabbaths holy (Leviticus 19:2-3), so someone who refuses to obey His laws for how to be holy as He is holy is living in a way that testifies that the God that they follow is not holy, who therefore that their God does not have the same identity as the God of Israel.
The Mosaic Covenant teaching to love each other and believe in Jesus, so that is not a new plan. Jesus is Lord of the Sabbath, so that is part of his identify, and we should live in a way that testifies about the nature of who he is by keeping the Sabbath holy in obedience to God's command in accordance with the example that Jesus set for us to follow. When we do good works in obedience to the Mosaic Law, we are expressing our love for God's goodness, and by being holy as God is holy, we are expressing our love for God's holiness, so everything that the God of Israel has chosen to command was specially commanded for the purpose of teaching us how to love a different aspect of His nature, which is why there are many verses in both the OT and the NT that connect our love for God with our obedience to His commandments, and we can't love God by refusing to obey His instructions for how to love Him. Likewise, we can't believe in Jesus by refusing to obey God's instructions for how to believe in him, or in other words, we can't believe in God's word made flesh by refusing to obey God's word. We can't believe in Jesus by rejecting part of his identity.
In Exodus 12:38, there was a mixed multitude that went up out of Egypt with the Israelites, so there were Gentiles at the foot of Sinai, and in Joshua 8:33 Israel was inclusive of both the foreigner and the native born, so Gentiles are able to become followers of the God of Israel by following His law. All of God's covenants are in complete accordance with each other and the Mosaic Covenant is in accordance with the promise made as part of the Abrahamic Covenant. The obligation of Gentiles to refrain from sin is not dependent upon being part of a particular covenant is is dependent on God's sovereignty, and God has revealed what sin is through the Mosaic Law (Romans 3:20).
The you should agree that we are under the Law of Moses, but you argue against doing that, so you don't believe what he said.
If we love God and our neighbor, then we won't commit theft, murder, Idolatry, adultery, rape, kidnapping, favoritism, and so forth for everything else commanded in the Mosaic Law. Though ultimately God is sovereign, so someone would still obligated to obey God even if they don't love Him or their neighbor.
The Mosaic Law is the Royal Law of Love, so you are contradicting yourself. In 1 Peter 1:16, we are told to have a holy conduct for God is holy, which is a quote from Leviticus where God was giving instructions for how to do that, which includes laws that you've personally decided are ceremonial. Likewise, in 1 Peter 2:9-10, Gentiles are included as part of God's chosen people, a royal priesthood, a holy nation, and a treasure of God's own possession, which as terms uses to describe Israel (Deuteronomy 7:6), so Gentiles also have the delight of getting to obey the instructions that God gave to Israel for how to fulfill those roles. It is contradictory for a Gentiles to want to live as part of a holy nation while not wanting to follow God's instructions for how to live as part of a holy nation.
If we do not obey God's laws, then we are sinning and are acting immorally.
All of God's laws inherently deal with morality and for you to claim that some of God's laws do not deal with morality is to claim that God made an error about what ought to be done when He gave those laws. You personally deciding that someone of God's laws are in regard to civil duties, health, or ceremonies does not mean that they do not also deal with morality. For example, we have a civil duty to refrain from committing rape, but that is also a moral duty.
Paul said in Romans 3:31 that our faith does not abolish God's law, but rather our faith upholds yet, yet instead of upholding it, you seek to abolish it, so do you think that Paul lied? In Jeremiah 31:33, the New Covenant still involves following the Mosaic Law.
Again, I don't see any grounds for thinking that what Jesus commanded was contrary to what the Father has commanded, but rather Jesus is one with the Father. Jesus obeyed the Father's commands and he was not hypocritically suggesting that we should only do as he said, but not as he did.
Do you agree or disagree that we should follow what Psalms 119:142 says is truth? Jesus embodied what Psalms 119:142 says is truth by setting a sinless example for us to follow of how to walk in obedience to the Mosaic Law (John 14:6) and the way to follow the truth, to believe in Him, and to love like he commanded is not by refusing to follow his example.
In Exodus 12:48, a Gentile was required to become circumcised in order to eat of the Passover lamb.