I really haven't assigned bedrooms to the characters yet. I have quite a few available, and will definitely keep that in mind. The posters I can get. The mess....not sure how to create that yet.
dForce with a few basic primitives and fabric shaders work wonders for anything you don't need to show off in great detail. I frequently use a small cube with about 6-12 divisions per ft depending on how detailed you need it to be. Cubes & spheres work well since they're not paper-thin like a plane primitive but you can use plains too if you use decent textures and the right displacement map but you'll want to only use a few with displacement maps to avoid killing your render time.
The second image in the following link is a quick example, the "dress" at her feet is just a cube primitive using dForce and a metallic blue car paint shader.
You must be registered to see the links
A lot of clothing assets also work well as props. Shoes & hats are easy since you can just convert them to a prop, anything you want to use dForce on will depend on the base model since dForce can freak out on models with mixed materials that weren't designed to be used with dForce. Just put them into the scene without having your character selected and use the scene identification settings to change it from wardrobe to a prop, apply a dynamic surface to it and simulate until you get the results you're looking for. You can move items around after the simulation has run but it isn't always easy so plan ahead.