All Things to All Men

For though I be free from all men, yet have I made myself servant unto all, that I might gain the more. And unto the Jews I became as a Jew, that I might gain the Jews; to them that are under the law, as under the law, that I might gain them that are under the law; To them that are without law, as without law, (being not without law to God, but under the law to Christ,) that I might gain them that are without law. To the weak became I as weak, that I might gain the weak: I am made all things to all men, that I might by all means save some. And this I do for the gospel's sake, that I might be partaker thereof with you. (1 Corinthians 9:19-23 KJV)

James Hudson Taylor wore pigtails and Chinese clothes in order to win the Chinese to the Gospel. He said, "Let us in everything unsinful become like the Chinese; that by all means we might save some."

Are there any limits in the "all" part of the things?

You can be all things to all men but you must abstain from all appearance of evil.
Abstain from all appearance of evil. (1 Thessalonians 5:22 KJV)

You can be all things to all men but your things must not be worldly things, which you have to ask your convert to hate (or love not) or separate from when he or she becomes a Christian.
Love not the world, neither the things that are in the world. If any man love the world, the love of the Father is not in him. (1 John 2:15 KJV)
Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you, and will be a Father unto you, and ye shall be my sons and daughters, saith the Lord Almighty. (2 Corinthians 6:17-18 KJV)

We are free in Christ, but we must not use our freedom to sin.
For, brethren, ye have been called unto liberty; only use not liberty for an occasion to the flesh, but by love serve one another. (Galatians 5:13 KJV)