No, because Paul specifically refused to have Titus circumcised and the entire issue at the Counsel of Jerusalem was whether gentile Christians would have to follow the law, particularly be circumcised. Paul won - the outcome of the counsel of Jerusalem was that gentile Christians were not bound by the law and circumcision was not required. Please read the book of Galatians, it covers all this.
And no, Timothy was not sinning when he was circumcised. Romans 14 deals with this and if someone not bound by the law chooses to follow it they are not sinning. Paul just calls them weaker Christians. Finally, no it is no a sin not to tithe. Spreading the Gospel has nothing to do with this issue. Whether or not one chooses to tithe has nothing to do with their effectiveness in spreading the Gospel.
This is, again, a logical fallacy because it presumes that I have not read the book of Galations. That would be an error. As I clearly responded to you earlier, "Galatians is talking about relying on works of the flesh (including the law) for salvation. It is not, IMO, teaching that the law is bad for you and has been abolished."
Again, the question for Timothy's circumcision (a requirement of the law) was whether it would help spread the gospel, not whether it was necessary for salvation. To throw out tithing because it was a requirement of the law and is not specifically required in the NT when it helps spread the gospel is getting on the wrong side of the Scriptures. This would have meant that Paul would not circumcise either Timothy or Titus. Yet Paul did circumcise Timothy. Obviously Paul could distinguish the two correctly.
"Romans 14 deals with this and if someone not bound by the law chooses to follow it they are not sinning. Paul just calls them weaker Christians."
Romans 14 also says "Each of them should be fully convinced in their own mind." and "if anyone regards something as unclean, then for that person it is unclean." If a brother believes that not tithing is a sin, then it is a sin for him. If you think you are the stronger Christian and do not need to tithe, then why do you quarrel with what you consider the weaker Christian over disputable matters? Are you not on the wrong side of Scripture yet again?
"Spreading the Gospel has nothing to do with this issue. Whether or not one chooses to tithe has nothing to do with their effectiveness in spreading the Gospel."
Spreading the gospel has everything to do with this issue. The brother who is compelled to submit to the OT requirement of tithing is helping spread the gospel in the same manner that Timothy was convinced to submit to the OT requirement of circumcision to help spread the gospel.