Keith and I are playing exclusively with the keyboard at the moment, just FYI. We both grew up as keyboard-only players before the mouse was popular (at least, I know he was into some games that were keyboard-only). We haven't even added gamepad support yet, honestly. It will be in before alpha, but he game is fine without it.
Once that's in I'll probably play with the gamepad when I play for fun, because I like the feel a gamepad brings to such a game, but for testing I expect I'll always be keyboard-only. If you're comfortable with keyboard-and-mouse, you'll be just fine with keyboard-only. You use your mouse hand to hit number keys to fire off spells, for the most part, if you want wasd. So far we are using mouse hand for he arrow keys and left hand for the tab key and the number keys, though. As in old-school games. This has the same keybinding support from ai war, so you can make it comfortable to you.
A gamepad is definitely NOT required unless you like that gamepad experience. And I imagine those who do already have a gamepad, or wouldnt mind getting one. Hope that makes sense!