The players won’t care about how pretty you make your maps. Make them functional and ugly, and you’ll save up so much time for other prep.

Whatever you do, don’t mix up who the killer is behind the scenes just because the player guessed it correctly before you wanted them to.

I use Gimp and just hand-draw everything. I’ve learned that players don’t really care too much about maps, so going above and beyond with high quality, ultra detailed stuff is wasted effort unless you derive joy from the creation process.