I would say that most of my parts are 200-500K also.
Assemblies range a lot more (and really depends on #of parts, patterns, and constraints)
.idw files will grow very fast with addition of iso views, (even more with shaded), detail views, sections of details, etc....I have an idw file that is 5MB from an assembly that is around 450K.
The number of files (and associated disk space) grows extremely fast once you start using it full time.