What size electrical wire do I need to feed a 90 amp subpanel in my attic?

I am finishing my attic into a theater with a wet bar and an additional bedroom. I would like to get a 90 amp subpanel up there to feed everything. My main 200 amp service panel is on the outside corner of my house. The subpanel will be located in an unfinished closet area beside the theater. I plan on going out of the soffit on the side of the house in 1 1/2" conduit straight down and punching into my crawl space to come out right under my existing service panel. Do you see any issues with that? Also, what size and type of wire should I use for that? I do not have any open breaker slots in my existing box so they will need to be condensed to provide for the 90 amp breaker for the subpanel run.