I think what Gunn was trying to say is that if you don't agree with his canon he doesn't care because it's all fiction anyway. However, he is trying to create a distinct canon for the DCU.
Yes. In the animated series Starlabs made a suit for Superman that blocked the radiation of Krytonite. However, the Joker's acid was strong enough to destroy the suit so...
I just finished watching the first season and kept my eyes and ears open for any dates but haven't come across any yet.
Maybe season 2 or 3 will have some though.