Print out posters/photos you like, especially for bands and such. Definitely look at secondhand stores for décor and stuff. You can go to secondhand record stores and buy shitty records to turn into wall art, i like hooking up the record to a motor than pouring paint on it, makes a cool pattern. The records look cool on the wall undecorated as well. You can also makes bowls out of records if you heat them up.

I just wanna say your room sounds awesome and good luck with it