Single servo for the steering. If you plan to race. Get yourself some new rims and tires. Boa C and Holeshots from proline are the top two tires of choice for indoor.

Anything besides that is up to you. The truck is good right out of the box. So everything else is up to the racer to decide.
Myself,I have RPM arms and carriers(bigger bearings over stock) and Tenko rear adjustable arms. Tenko battery/RX/tank mod. GTR shocks.