I have a 1995 BMW R1100GS. You could do almost anything to that motorcycle using the toolkit that lives under the seat.

The one exception is checking the valve clearances; that requires feeler gauges that weirdly aren't included (although the kit includes feelers for the ABS sensors and valve checks are necessary every oil change). I haven't replaced the final drive lube because, without removing the rear end, it requires suspending the motorcycle vertically, although I have siphoned much of the lube out and replaced that.

re transmission -- someone told me a long time ago, you really do not want to open a transmission

A manual isn't that bad, and I know people who work on them, but the main problem is that they're just an entirely different set of tools and techniques from just about everything else. You need a bunch of different tools for "rotating part" assembly and disassembly, and a bunch of different skills. Mostly, manual transmissions don't fail randomly, though.

Automatics be black magic boxes that will fail expensively, though. :/

Precisely this. If you don't need to actually rebuild a manual and just need to get to a seal that can only be replaced by cracking the case apart, it's not that bad. There just isn't that much to a manual.

Keep it clean, and work with care and diligence, and you're probably not going to get in truly deep shit.

I'll second that a manual in normal service is unlikely to fail catastrophically. The synchros can wear or the transmission can start popping out of gear, but they tend to experience graceful degradation, and the control software is sufficiently adaptable to work around the quirks.

Not true at all. They do have a scary reputation and unlike a lot of other vehicle maintenance, you need to be very aware of cleanliness. But they are just mechanical devices. They can be taken apart, worn components replaced, and reassembled. Watch Gary Ferraro on YouTube if you're interested.