Nothing wrong with suggestions. Sometimes I get good ideas from those when I'm stuck by giving suggestions a spin and end up with something completely different I wouldn't have thought otherwise.
Secret rooms being separate maps would work perfectly. I'm probably adding some sort of vault system as well at some point so that could work for it too. I've been also thinking about those hidden areas for extending the dungeon for optional branches.
On that note, I'm probably at some point extending the main game as well. I already know how the plot would continue, but I'm still struggling if it will thematically fit the game.
Alchemy would be basically blood + another ingredient like leaves or something similar to that. But mixing beer and wine isn't a bad idea as well. I'd probably add another alcohol type, spirits, so there'd be some variety.