I would get the following after experiencing some pains with mine:
1) steel pinion (largescalerc.com now has this and it is on ebay for 72.99 with a steel spur, you can't go wrong with this combo)
Eventually:
2) alloy diff housing (the plastic may be fine with a stock muffler, but with a tuned pipe, it's going to break eventually, which means the gears will probably strip out, you'll lose a dogbone and an outdrive, expensive to wait, cheaper to buy early and not have to worry about it again.)
3) large alloy motor mount
Those are really the only needs in my opinion. Someday you may get yourself the ball drive set which will eliminate broken dogbones. I have a posting on it in this area here.
Also, go to Tower Hobbies and purchase spare parts, they are cheap and getting about 40 bucks worth is a great thing to do before you even start running!
Also, look for a good deal on these, there are some clones out there that are priced right in my opinion. Knowing what I know now, I would have spent 500 bucks on a firehammer clone and then used the remaining 300 bucks on all the upgrades above.
The radios in these things are either good or they suck really bad. Mine was bad, it would glitch frequently causing the failsafe to kick on. Spektrum DX3 is an awesome radio replacement.