It all depends on what type of bulbs/lights you're going to use. The traditional spotlight bulbs emit a lot of heat and use a lot of power. I don't like dimmers but there are some available now that can be used with energy bulbs, cheap to run and you could fit more lights than you'd ever want.
You could also consider halogen lights. You can run multiple bulbs of one transformer. If you use enough of them you'll get well spread light without dark spots in the room. Instead of a dimmer you can put all the lights on two different circuits so the lights are controlled by two switches.