A. Yes, and Yes and
Comments: Virago petcocks are made to run with the vacuum created by the engine when it's running. Starting is handled by what's already in the float bowl on the carbs. "CRCII" has the petcock rebuilding kits available. Other places sell Kawasaki petcock rebuild kits. They work fine, as the petcocks are the same, only the direction of the fuel/vac lines are different on the Kaw version.
Comment: You can run your bike by leaving it set on PRI, but when tyhe bike is not running, there is nothing to stop the fuel from getting to the carbs. If you have a sticky float valve, you could have a problem with fuel in the oil, or a leak that puddles gas on the ground under the bike, or both. I don't recommend it, although some here in Virago Tech do. I suggest rebuilding the petcock(s) as it is an easy task - about 15 minutes from start to finish. Some things are better repaired and left stock, if you're keeping your stock tank.