Id take it easy on the sand paper. Maybe emery cloth but a good surface cleaning to get film build up off is all that may be needed. Unless the surface is glazed were slippage is magnified, I wouldnt feel the need to rough the surface. I do us a bit of sand paper and brake cleaner to rough up the clutch pads a bit.
Be careful of getting sandpaper grit into things like needle bearing etc and thats why I would recommend emery cloth over sand paper but I dont think its needed for the bells unless they get glazed. I doubt you would throw them out of specs without lathe turning them.
Also, keep those variator faces clean with simple clean rag and alcohol or break cleaner.
Put a dab of grease in where the starter shaft fits in. Maybe a touch of grease on the kickstart gearing.
Maybe a finger of grease into the needle bearings.