That's actually not too hard. You'd just have to set up the houses using Upper Layer tiles within a bunch of events. First page is blank, second page is the house tile (with a switch to activate it, of course). Then, whenever you "buy" that house, it'll appear within town.

The "advertising" would just bring in a set amount of people over time. Say, 3 people, one every 7 minutes for the "advanced" advertising, and 2 people, one every 12 minutes for the cheaper version. You'd have to buy new advertising in various stages of the game, each bringing in certain people. Of course, that's just my idea of an advertising system, but the idea is to trigger those house switches so that everyone has a house to live in.