GypsyComet
SOC-14 1K
people hollowing out asteroids and living in them is a well-established SF trope.
In a setting like this one, belts are going to run the gamut from gravel fields through accreted bodies to, at least in the areas affected by the Final War, flying mountains.
By TL15 there are likely ways available to take a rockpile asteroid and apply heat and make it a unified mass. Between gravitics and fusion it should be very doable.
In the short term we can probably infer something about a belt's composition and size distribution from the settled population, even if they are only trends.
Low Pop belts stand a higher chance of being gravel belts, IMO, since you must import *all* living space at significant expense.
High Pop belts are more likely to be Flying Mountain belts, since viable frames for living space are common, and each flying mountain can be settled to a high density.
As the TL climbs, the accreted body belts will become more viable at all population levels.
The asteroid types are also likely more common in certain positions. Because of their origins, gravel and mountain belts are going to be limited to actual belts, though the loners on highly eccentric and/or off-ecliptic orbits are also probably mountains. If you want to tweak the amateur astronomer in your group, put a mountain or two in the local gas giant's Trojans, which *should* be accreted most of the time. Trojan Points, particularly those associated with jovians, are locations of forced proximity, so accretion is almost an observable phenomenon. A Mountain in one of those locations is an oddity, especially if the system doesn't have a Mountain belt elsewhere...