Just a few inputs
When you take out the body, take extreme care off the micro steering, don't touch the steering bar or even the steering motor.
The steering motor has an helicoidal pinion that is only "laying" on the steering bar. Misalignment of the ST motor can be fatal to the steering as it risk to disengage permanently after the operation. My Sylvia had this problem, steering was not responding again until you pressed on the hood
to reengage the ST motor
Also handle the rear motor pinions with care, and in general, don't apply force to the wheels, the axle are very soft.
For the battery no problem, just good soldering and insulation of contacts with tape is required.
Good luck
