Quote Originally Posted by Lemons
Sorry Spartan, but I forgot to answer your question. You get a province when a faction city rebels and becomes independent, and as far as I know you can recruit every unit in the game as the slave faction, and are ONLY LIMITED by what region of the world you recruit in.
At the beginning, playing with slave faction you have all the regions assigned in descr_strat. It's difficult because is (usually) a large number of regions and you get bankrupt easily.

Regarding units, it depends on the assign in export_descr_units. There are units of playable factions that are not allowed to rebels, usually elite units. And (if I remember well) in each region you can recruit the units corresponding to the "default faction" (or something similar) coded in descr_regions (again if I remember well).