If you are stuck, my tip for starting out is to basically find a similar robot that someone else has designed, and modify thier stats into your own, leaving motors and more technical things alone (which should be fine, as youve picked soemthing approprite) Im not saying copy people, but take advantage of the knowledge of others until you get your footing.

The other trick with weight is to have a sort of mental checklist of where your weight is going to be distributed - take weapons, armour, drive and give weight accordingly. There are not any robots with tornados power with a huge disc, but if you dont have any weapon then that gives you lots more weight for armour. Its just finding the balance with what you want.

The last ip is that its usually not the most powerful bot that wins overall - its the most versatile. Unless its Aaron.