Hatchet, Sams robot, runs on a 4S lipo at 14.4v. That drives the 12V drills and that motor. Its not amazing but it can give a good thump regardless.

The best esc will depend on your budget. Hacked TZ85A's are the top notch for most builds but they are over kill for a single drill. I would look at these: http://www.botbitz.com/index.php?rou...&product_id=74
If you buy 4, thats one for each drive motor, one for your weapon and one spare. its just easier to use the same type for everything. You may want to add a bigger heat sink to the weapon ESC to keep it cool.

Run it all on 4S else you will run the risk of burning out your drive motors on 5S without adequate cooling.

Most people get their plastic from Direct Plastics but I am not sure if that will be your best option if you are not in the UK.