I like the idea of a remix. I'm not sure I could do it myself, but looking at it that way is wonderful!

I think I get what you mean about having the same premise and then seeing a similar fic and being all "eeeeh, can I post mine now?" I think the answer should always be yes, because just because two people had the idea, doesn't mean one shouldn't be shared.

I've decided to go and ask, if I do remember where something is from and then credit them in the author's notes. I'd rather be over cautious than get called out for plagiarising someone's idea, when I didn't mean to.