6 Robots I think would be ideal, that's enough for a really good annihilator!
Glad you love the idea of a commentator! I feel it would be a great addition to the game in terms of audio!
Can't wait to start building bots either! I can this drawing in a large community, and I'm sure many tournaments will be held.
Another cool thing to do would be to add a camera that follows behind the controlled robot, maybe even splitscreen for more than one player controlled bot? This seems like an ideal game for local multiplayer, as so many games don't offer it any more on PC.