Hills aren't an issue, I live in FL. Bridges, on the other hand, can get quite steep.

Yes, its a 9 speed. I was thinking 11-32 might be good, but wasn't sure it would work with my derailleur. The spec sheet for the stock build calls for an 11-32, but it came with a 12-23.

Also, when choosing a cassette, how do you know if its for road or MTB?