Well I do not have a bike like this that is why I held off. However since you have not gotten anything else, here goes. The following is a list of common things.
1: these bikes are air cooled, they are not as quiet as a water cooled engine. You will hear strange noises. Valve noise is fairly common but grinding or clunking noises while starting or running are not.
2: Check the wiring connections as best as you can. Look for badly worn wires or corroded connectors.
Check your controls to make sure they work right.
3: Check the tires for age cracks. If they have a lot of little cracks, they are needing to be replaced. The cracks are hard to see so look closely. Also, push on the rubber tread with a fingernail, you should be able to push it in a little. If you cant, the rubber is hard and needs to be replaced.
4: A BIG one here. Buy a compression tester. Does not need to be a big expensive thing. A simple $30 tester will work. Test the comp on all 4 cylinders. now I do not know what the DOHC engines should be at but a rule is never get anything below 110 - 120 unless you are prepared to tear the engine down.
These are basic for any bike that is air cooled unless you are getting it for dirt cheap!
The ride IS the adventure. The destination is just to get gas!