My advice would be to go ahead and replace the belts, bearings, some u joints, etc. with new, right now while it is in the shop. Then you have all the old ones as spares.
The wheel bearings at the front and rear of each track are the most critical as when they fail you are pretty much dead in the water and have to de-track in order to repair.
I'm not a Tucker guy and have no experience with them but I learned right away with my first snowcat that preseason maintenance and daily pretrip inspection is critical to a safe trip. I treat them as I would an airplane and my life depends on the cat getting me home each time. You can easily and quickly get into some serious back country where rescue is difficult and not readily available. Sounds like you are already thinking along those ideas.
I also carry a SPOT tracking device that others can follow my trip and I can get emergency response in a worst case situation. There are a couple different brands out there and some have text capability.