Paint Ball....
I would suggest regulating it as a Special Use Permit for a private recreational facility, similar to an archery club, gun club, etc... in the most rural district the county has. Although, paintballs aren't lethal like bullets or arrows, they tend to alarm those people who are not familiar with the activity. Generally the paint balls will not travel more than a couple hundred feet at best, and at that distance won't have the velocity to even break the outer shell to release the paint. It is an adrenaline rush, so expect yelling, and the guns do make a little bit of noise. If in an agricultural area, I wouldn't worry about a buffer. The size of the field would be limited by the SUP, but will likely be several acres in size.
In regards to parking. I would bases it on the number of courses the petitioner tends to have, or see if they have set a limit themselves to the number of players they would allow at any given time. In addition, see if they will serve refreshments, have a store, etc... Then base it on 1 space per 3 people and whatever the county uses for calculating parking based on square-footage of retail space.