Really, I don't want to keep you from having fun in CAW, but if your SP settings somehow glitch, you can specify for each lot that you want to keep empty that SP isn't allowed to push sims there or use it for the usual stuff. I've never seen those settings being violated.
The SP settings that completely disallow homeless from moving into houses are usually also respected by the game. The only time I see those violated is if you use Traveler to switch homeworlds, and at the very start, the game may get a move in, before SP starts running properly. Other than that, empty houses will stay empty.
By the way, there are lots of worlds available with about 14 residential lots. Several by Rflong7 or Norn come to mind.
