I play on huge maps. I usually go for for 5-6 cities initially, depending on how many good spots (luxuries & multiple bonus resources, fresh water, etc.) there are around my capital. After that, I let my population and economy stabilize, and when the late game resources start popping up, I look for more overseas spots as needed.
I mentioned this in another thread, and it bears repeating here:
The tech penalty for # of cities scales down as map size increases. It's 5% for standard maps and 3% for huge.