Well, damnit! I spent almost an entire day yesterday planning out the game's world. Previously I had a basic skeleton just to get me started, but now I actually have the whole thing more or less laid out from the beginning to the end, and guess what - it's HUGE!
For the later branches of exploration I didn't even bother to plot "explorable rooms", as it just got so complex - I'm sure this will bite me in the ass eventually - but I'll cross that bridge when I get to it. Furthermore the area tileset coloring is subject to change, as I am now leaning toward dividing the game into distinct worlds ala Metroid's Norfair, Brinstar etc, and analogous Castlevania castle wings. The number of health and mana containers is also a subject to change, as I am now debating if I should find a way for the HUD to accomodate more than 5 of each container.