If you're liking P3, you should enjoy P4. To me at least, it takes all the good from P3 and makes it better, but not so different so that it's still familiar. If you have access to a Vita, P4 Golden is the way to go!
I've never really thought on creating fictional holidays. I'd rather create a brand new one than use an actual holiday character in a made up world though.
Some of my favourite parts in books are later parts explaining why something happened at the beginning. I think so long as it gets explained well, it would be fine. It will get the readers going "oh, so that's why!"
Meh, I think with the millions of things that have been written by now, it's going to be never impossible to write something tha doesn't borrow from something else, whether you mean to or not.
Many times I'll be watching something and my jaw will drop because they did something similar to what I...