I would definitely invest in a high-torque steering servo. While there are some that go up to 200 oz-inches of torque (Airtronics 94258), if you get a quality ball-bearing steering kit you won't really need too much torque, since the steering will be more efficient than it would with mere bushings.
An old racer's trick is, once you get an aftermarket steering servo, to replace the stock throttle/brake servo with the original steering servo. More torque for better braking, you see.
RPM skid plate covers are a good idea.
Use NiCd or MiMh 1000MAh receiver batteries.
Break in the engine as per stated in the manual. You'll be rewarded with a sweet-running and powerful mill. The stock pipe is fine (
XR2PROBE, the AE will not work on the 2.5 header due to its downward slope). Wookie, I think that the stock plastic pipe is much quieter than that racket-maker on HPI's Savage!
Stock shocks are fine, I haven't touched my suspension settings for the past two months.
Where are you going to run? If you're going to race the T-Maxx, almost nothing beats Pro-Line's Bow-Ties!