Random thoughts in no particular order:
Oh and I commend you for being prepared to throw out so much stuff!
-Since that one room is going to be a studio/office try to divide the space into zones either by using bookshelves as a barrier (they are really tall though--I was imagining turning them over on their sides and stacking them if they are the same size--prolly too wide for that though eh>) or just doing it visually somehow with a rug, etc.
If you can spend $, I really like this shelf/room divider from IKEA:
-Pretty up the bookshelves by having some baskets or nice colorful boxes on their for your arts and crafts or photos or whatever. Can also have a few treasured on there, framed pictures of fashion stuff or whatever you like, some books lying down and some up, etc.
-Do you have a table for doing your art stuff or will that be the desk?
-I agree with covering the pink plastic looking wall or painting over it...
-As far as the bedroom, remove a lot of that stuff sitting on top of the surfaces for a cleaner look?