models between 2k and 5k for main characters,
skin size around 512² up to 1024²
level: try to stay as lowpoly as possible for your collision model. if you want to create detailed structures, use a simple box for collision if you can. the speed f the level depends on how many polygons, shaders, particles, models etc are visible at the same time. so use LOD and (self-scripted) vision occluders wisely.