You need to understand how much more time consuming and complicated it is to build a featherweight than an antweight.

I'll back up everything Will has said and I certainly agree with all the advice he has given you. There is nothing to say that you won't be able to build a more powerful robot in the future, but it would be a good idea to gain some experience beforehand.

I'd say get your hands on some good, reliable drill motors (preferably dewalts or something similar) and use that as your drive. This is the basic setup we've used in Annihilation and that's been running since 2007, fairly successfully and has recently been performing even better with the new A123 cells. Just because something is simple does not mean that it won't work well. We haven't even taken the drills out the cases, and they're only held down by two straps of rubber. Pick the right parts (not always the most expensive ones), build it reliably, keep it simple and drive it well and it should do fairly well.

Another matter is that the robot is not the only aspect of winning. It is also important to be able to drive your robot well, which I can see as rather challenging with a lightning-quick pusher, Explosion is bad enough! Building a simple pusher does not necessarily stop you from winning, as many have proven before.

Good luck and have fun.