The free checks come first
Remove hair from axles. Check for body rub, bent parts and tight bearings. Make sure the steering returns freely and the rear pod moves without binding. Confirm the pinion and spur mesh using the manufacturer’s procedure. A car with friction or inconsistent steering cannot provide a useful setup baseline.
Spend only to solve a problem
Tyres suited to the surface are a logical early purchase. Replace worn bearings when needed; many cars already include them. A T-plate change can alter rear response, but the effect depends on tyres, grip and damping. A kingpin flip is a platform-specific modification, not a universal upgrade: check clearance, travel and the relevant build instructions first.
Make a simple test plan
Run a short baseline with the same battery condition. Record clean laps and the handling symptom. Change one item, then repeat. For DIY, begin with non-critical pieces such as a parts tray or setup gauge. Printed structural parts need suitable material, orientation and fit testing. Do not treat an untested print as a proven race component.
A useful upgrade solves a measured problem. Everything else can wait.