3- it all depends upon which car oil you want to use - look for the JASO rating or use an oil like Shell Rotella 5w-40 which although a synthetic diesel type oil is great for bikes [ it does not contain the friction modifiers that cause clutch problems and is shear stable ] .Generally speaking car type oils are not a good idea in bikes because they do not contain enough zinc compounds .
A high quality ester based synthetic will allow you to extend your oil change intervals .[Amsoil and Mobil 1 for instance ]
Blessed are the cracked, for they let in the light. - Spike Milligan
"When you come to a fork in the road ,take it ! When you come to a spoon in the road ,take that also ."