As far as crew size goes:
Tiny hull - 1 or 2 crew, seems to vary, with noncombat craft usually having 1 and combat craft having 2 - maybe the second is a gunner?
Small hull - 5 crew
Medium hull - 25-30 crew, again, apparently varying between ship types
Large hull - Varies widely between around 200-400 crew
Huge hull - Likewise varies between around 1200-1500 crew
Ship length and width seem based partially off of what hull is being used. This might also relate to the crew size.
It's possible that the GC2Types.xml file can be edited to change these. While I'm not certain, it does have the descriptions for components that you have when looking at a ship's details.