Depends how thorough you want to be. I'm not aware of anything which specifically needs to be checked after swapping out the tach roller, but I haven't checked the manual.
If the tach roller has gone bad, I'd check the pinch roller too (how did you sent Terry payment, by the way? That's always been the showstopper for me)
Other things which you'd probably check if you were doing a complete full service include the tape speed (a frequency counter and a test tape should work), pinch roller pressure, the amount of tape tension in various modes (play, rewind, fast forwards). IIRC a rough guide on TASCAM machines is that the tension arms should be roughly halfway in their slots, once they are settled. There are a couple of
servo adjustments for that if it's way out.
You've also got head alignment, and the electronics but with 24 tracks to check that's not going to be fun, and again, it would need a test tape. To be completely honest, I haven't done much to mine yet since it's working well enough at the moment. (Though I should really check the winding tension on mine at some point, it seems to be a bit slack when stopping sometimes).