I think it should still be possible. Cors is enforced by browsers, not server side. Meaning your client cant make a request to lemmy.worlds backend BUT, your client can make a request to your backend which can make a request to lemmy.worlds backend.
The site I have this hosted on is actually connected to lemmy.world, not my instance
Yes, definitely will do.
I think I know this issue. When clicking a post from the front page it stores the post so upon landing on /post/xxx it doesn't have to refetch that data. It fetches the comments on /post/xxx but not the post itself. Just need to fetch the post itself if someone lands directly on that page.