Here are my thoughts on the doujin rumor: as it stands, taking the 1st post at face value it's probably fake. If we were supposed to take it that Reimu was in development at the time it was initially posted, then too much time has passed. I'm sorry but Covid delay or not, I don't believe it would take 18 months to develop Reimu, no matter how complex the concept. In that time span she should have been in FP1.
At least, I think Doujin Leaker timing fits because he got the "information" around the period during which ZUN was apparently trying to negociate with Nintendo and around the time FP2 was being validated. So he would simply have heard that the deal was successful, but he wouldn't be able to know when Reimu would come. For all we know, a deal around summer 2019 could be the last deal made for FP2, since it was confirmed around that time. This could mean Reimu is the last character, or at least not in the first three (if they are still developing three at a time). She could also be the reason why the pass has 6 characters, maybe they had already 5 characters planned and then ZUN came and said "hey I wand to join too".
The rest of the leaks are probably only rumors, but the fact the Doujin Leaker has had some real information at some point is definitely a good things for us.