+1 on all the rubber parts.
The rear in particular is under a lot of strain under track driving. There is a toe link where the bushing is under constant tension.
Oil changes should be done sooner than every 6 months if you track. I recommend doing a UOA to verify, based on your modifications and driving habits. However, seeing that BMW’s factory fill Castrol 10w60 sheers to a 40 grade within 1500 miles of street driving, a 5w40 in a car with a stage 2 tune is going to see some very tough times.
I change after each track day. Depending on what oil temps I hit, I may stretch it out to every other track day. But 6 months seems very sketch, and definitely is not race car
I’d also do the rear diff every 2 years if driven hard on the track. Coolant I also do every 2 years. Same with tranny fluid. The temps that the diff and transmission gets to is very high–being awd and devoid of any sort of tranny cooler. Most 2wd cars without coolers get scary hot as is already.
I also check tie rods and wheel bearings after each track day for play. And inspect brake lines, the hard fittings at the ends of the lines, rotors etc after each day.