So getting right to it then, what type of foundation are we going to build for our flagstone patio: sand, cement, or gravel?. Short answer: well it depends. Quarry screenings (if available in your area) are generally best for under the flagstones.
Forget everything you know about driveways. Asphalt, concrete, crusher run gravel, rail road ballast, paving stones... If you have a long driveway, or if you need a system of driveways on a farm, and you are planning to go with those common methods of paving a driveway, you are going to need a separate mortgage just for the driveway (or driveways).