You could try putting your perspective focus point in the centre and have perspective guidelines radiating out to help you figure out the various angles of objects / rooms. The ladder in the narrow room for example: the rungs at bottom or top are visible depending on the height position. The lights in the large room won't look wonky if you use the perspective guidelines properly.
That narrowest room I think is a bit too narrow. Try to put a bit of space around the ladder. This way you have enough for side entrances or shelving to store gadgets (makes it more interesting).
Using a vector program makes it easier to do all those perspective lines. Once done you could just import your rough work into a paint program for more finishing touches. I use Inkscape (vector program), GIMP & KolourPaint (both art programs). I think KolourPaint & Inscape are linux only.
Hope these images & links are a helpful:
LARGE ROOM (better perspective with central focus)
NARROW ROOM (perspective for better ladder looks & spacing).
DRAWING
Successful Drawing by Andrew Loomis (refresh if doesn't load first time).
http://fineart.sk/photo-references/andr ... ul-drawing
MUSIC
Have you tried DST's music site?
http://www.nosoapradio.us/
http://www.freesound.org
You can filter by tags and license types (creative common stuff too).
Here's a list of Dark tagged themes: http://www.freesound.org/browse/tags/dark/
Good luck with project
Got the Gollum bug). 
