I would keep it a little far away from houses or roads just to be safe. Law enforcement permission is a MUST. You will also need to have insurance for anyone that may get hurt or property damage or state that it's a "Play at your own risk" field and have strict rules.
As far as rules, Just compare it to some of the other fields here on the forum. Whether it be field or CQB rules.
One rule that is a good idea is to have a gun bag policy since it sounds like other people will be able to see people driving on and off the property. Law enforcement will also appreciate it too...
Just look around on the forums and see what rules sound fair to you and what you need to do.
Another thing is to have tables for people to put their gear, guns, etc. Bathrooms, Maybe even a little food trailer if you will be open during lunch or dinner hours. You may also want to open a little "Pro Shop" where people can buy more BB's Green Gas/Propane, Etc.
Other than that I would just put up a barrier around the whole property or put up nets that would keep it more private and kind of keep BB's from flying farther than you want them going.
A respawn area is a must, That would be where the tables and everything would be. I would probably put up walls around that so no one gets hit if games are still going on.
Edit: Also, A decent admission would be good to help pay for all of this
I wouldn't get too expensive or people will just pay the extra and just go to one of the bigger more established fields...