He is a heretic and the debate is not complicated at all. Anyone who advocates and justifies for non-Jews to take on religious observance of Jewish commandments is misleading Gentiles. Every single one of my Noahide friends agrees with Rabbi Weiner and disagrees with Katz.
He has a whole explanation and it's a Torah debate. I was against him teaching kaballah to Gentiles, but I'm not a Rabbi, these debates involve many sources I have not studied for years, so I just try to stay friendly with both sides. A heretic outright says something forbidden is permitted, he's saying Torah says it's permitted and has sources and there's a debate to be had there. It would be easier to have it if he didn't use cryptic language for mundane things.
No ban on marrying cousins in Judaism many of the admorim are married to cousins.
The Lubavitcher Rebbe,ZT:L,ZY"A was married to cousin & she didn't even have to change her last name when she married him.
There's like a Rabbi or two that did it, I meant to say marrying your aunt is widely not allowed nowadays. Cousins is still allowed but I've heard Rabbis not recommend it.