On the smaller question about the mixed fiber: If your Bible has cross references, there is probably one pointing to some verse in Exodus, about the fabrication of the veil which covered the Holy of Holies. The mixture which was forbidden in profane use was the one which was used for the veil. So, that mixture was reserved for that use only. I didn’t figure this out myself, I read it in some commentary.
On your main question, see
ewtn.com/library/CURIA/PBCJWSCR.HTM.
This lengthy document explains, in an introductory way, how some OT things were retained in the NT, some were replaced, etc.
There is a Jewish commentary on the New Testament called The Annotated New Testament. There’s a lot of helpful information in here, on questions such as this – helpful perhaps not always on a specific question, but in general.
Jesus seems to underscore your position, see Mt 5:17 up to maybe verse 24 or so. But, the key here, is the issue of if, when, how, and where the old law may have been fulfilled by Jesus, which it was. So, taking all of this together, one may loosely say that as Jesus fulfilled the righteousness requirements of the law, the ceremonial or cultic requirements such as sacrificing animals, were abandoned. But, the righteousness is never superceded as the cultic requirements were.
Your specific questions about homosexual relations have been addressed by others, above. There are still people who, like yourself, question whether the prohibitions were mendable disciplines or more rigid and unchanging in nature.
There is no central authority (or “magisterium”) in Judaism, comparable to the Catholic Church. As such, there is support for homosexuals in Judaism, without the harsh restrictions at the “law” otherwise imposes. As I understand it, Reformed Jews don’t even accept the inspiration of the Torah (including Leviticus). So, if it is already not a fact, there is certainly discussion about whether homosexually oriented persons may be a rabbi.