The TLT-1 is not too demanding on servos since it is small, and the servo(s) are mounted close to the wheels. I’ve used the standard, cheapest servos and had decent results, but I’m not that picky.
The motor, battery, and electronics aren’t included. We’ve run one off of an Orangutan X2; if you use one, you might want to use more than 6 cells since the voltage drops below the X2 limit pretty quickly. At full speed, the thing is quite fast, so I never went past about 30% duty cycle.
By the way, the TLT-1 has been discontinued by Tamiya, so the few that we have are all that are left.