Maintenance is all about personal preference. I replace parts when I spot something that doesn't look quite right or seems to have too much play. I check bearings once a month. Diff bearings get checked when I have the case apart which is pretty rare. I've only had 1 diff bearing ever fail on me and it was an outdrive bearing on an SC10.
I blow off the whole kit after every run, check screws, look for cracked parts, make sure my hinge pins aren't coming out (TC3 have a tendency to loosen up) and really that's about it. I'll check camber and toe every time I get to the track then keep checking it during the day, especially after a race that was rough.