My town is starting to look pretty crowded in places. What is the maximum number of NPC residents my town can have? Is there anything I can do to affect this?
You can have up to 10. 9 will move in on their own. You have the option of moving in a 10th in if you have built a campsite and are chummy with the visitor.
you can have a maximum of 12 villagers. They will move in when your town becomes "better" more trees, different fruits, lots of flowers, no weeds, upgraded stores, etc.
if you have 12 villagers and a new one wants to move in, one will move out.