glad you found the maps! they're not meant to be very detailed, so as not to spoil the interactions on each floor.
there aren't any plans to add to or revisit this game. I would have to revert back to previous GB Studio software to do so, as migrating the project to the current version I work in is out of the question. and, frankly, the game has done so poorly in all markets, it's simply not worth the time and effort, I'm afraid. but I'm developing new GB games all the time! ✨
lastly, if by a black arrow, you're asking about this mark on the menu screen down here, no. there's no hidden pages or anything. it's just to delineate the stats from your inventory.
thanks again!