How big they can get: Depends on the breed, 4 inches or so? not really sure.
Best breed for beginner: Dwarf or Syrian
How old they get: their average life span is 3 years
What exactly do they eat: hamster food and fresh vegetables daily, occasional treats

This is a *wonderful* website I used to frequently visit when I first got my hamster.
http://www.hamsterhideout.com

They also have forums. I posted there a few times but haven't in about a year ... that was when I got my hamster.
http://www.hamsterhideout.com/forum