The number per hall is a simgameconstant, as are their gender odds and minimum MRB rating to be hired. The lifepath nodes system from the Mechwarrior RPG is the basis for creating their backgrounds. Any more details than that are beyond me. RJPhoenix in the BEX Discord is working on a mod that alters pilot spawn functions a lot, so he's probably the best source. There's a mod on Nexus that alters the lifepaths so that their odds of being from each of the great Houses are lore appropriate overall instead of biased to the Aurigan Reach. That would teach you the basics of altering the existing lifepaths.