You have probably already thought of most of what I would do. Clean, Strip, paint areas not easily accessed while the cab is off. Assuming those areas would need it of course. If the trans, transfer, brake MC etc need serviced now would be a good time with the old cab off. Check condition of u joints, flanges, hoses. Also, prep on the replacement cab -all those hard to get to places that might need a little paint etc. check the cables to speedo, gauges and air lines under the dash. Also things might get damaged while removing the old cab so recheck before putting the new cab on.
You have probably already thought of these things, so my only other suggestion is to take pictures for others like myself to learn from please.