1) Gold version is a fairly cheap complete full version, think of it as the current supporter version but finished and more less "definitive". Lite version will stay up as a demo in Itch.io, Newgrounds and probably Steam as well. If you only played the free version, it will have the rest of the story mode, worlds from 5 to 8 with their respective characters and Hscenes, exclusives races and some extra stuff. It's also a nice way to reward us for our years of devs without having to subscribe, I know subscribe fatigue is real.
If you wonder it will also become the only way to access the full content as the supporter version will get eventually discontinued in favor of the Gold version and our Patreon/SStar money will instead fund our next game.
2) Due to recent itch.io policy i don't think it anytime soon. We are not against it, but we don't think the current state of itchio stance on NSFW games is worth the shot. We might also sell in other shops (i know some folks really want gog) than steam but this will be rather discussed later with our editor, we don't plan to be steam exclusive.