Nobody would question if you are ABDL or not.... theyre are a LOT of baby suits out there at the stores for halloween, but those look super fake. If you want to do this, I suggest getting your OWN suit. Such as a proper fitting diaper or a adult paci and things like that. Your risking quite a bit, especially if people think you are "To old for halloween" or how much you "Get into" your role. I wish it was a great excuse to grab the diapers and stuffy and go outside to play and get candy, but sadly this will probably be frowned upon. I may or may not try this myself however with a simple set of footies..........HOWEVER, if someone sees the footies are a little thicker, they will probably question you. Enjoy haloween, and remember, excuses, excuses, excuses.
P.S: To answer another one of your questions, to do a full house party, would take a lot of time and trust. HOWEVER, if you got a lot of trusted friends, pulling off a diaper halloween party may be a good time to do it as long as there is set rules to follow. Otherwise, if you guys go outside to the back for a BBQ, expect indecent exposure for the neibors calling the police. Warn them first if your going to have a party, rather than police kicking in your door for loud music and seeing a bunch of furries in diapers. You may have some trusted friends who dont mind showing, but the more stealthy kind may be to shy to show anyone else. Making arangements for both private and non private events if you have enough people may be ideal. A halloween theme, (Cute spooky or spooky spooky) will also provide a good excuse that your just having a halloween party still, in case you are going full stealth and are caught.
Hope this helps a little bit, and party or just going out for some fun candy's. I hope you enjoy the night and figure something out....its not that far away.