I'm with Kenny on this one.
6s is a LOT of power to run through this truck without any experience with it. Start out with 4s, running the 54T pinion that comes in the parts bag. You'll be running 40-45 mph with that setup. Way more power and speed than you need starting out, especially for bashing. Go with a set of batteries like the
SPC racing 8200 mAh batteries, and you can have great power, excellent punch, and outstanding run times. You can get (2) 2s batteries and (1) 3s battery, and once you get used to the truck stepping up to 5s is no big deal. It will probably be as strong as you want to run it. 6s puts a tremendous amount of strain on any MT, so do it only if you enjoy tearing the truck down often and replacing parts.
I would suggest stock Summit driveshafts as replacements, once the stock ones go out. The metal ones are overpriced and don't last any longer than the Summit shafts in my experience.