is it a Tenere? A Tenere rear sprocket is 45 as standard matched to a 15 up front. Personal choices, but I'd recommend a rear 46.

As for servicing, I'd humbly suggest draining water coolant and removing the radiator and, carefully, making sure the fins are clear of flies, sand and mice and flush out from the back to the front.

Whilst your tank is off and your doing valves, I would perhaps unclip and lift the main loom away from the frame and check for rub marks. Repair if required and if not replace with bicycle inner tube between the loom and the bike frame for protection, all zip tied in.

The rear sprocket carrier has its own bearing which makes 3 for the rear wheel. Whilst that's out, check the cush drive / sprocket shock rubbers for wear which causes early bearing failure.

Have a look at the clutch cable at the lever end for fraying.

It's all good fun..

__________________
I have a lot of growing up to do. I realized that the other day inside my fort.