Any heat source can be used that will produce 110F water, so you can hook up a car engine to drive a generator and make hot water at the same time if you wish.
The tubes used in floor heating are small so they have too much resistance to go more than 300 feet in 1/2-inch tubing. This means that there will be another loop for about each 150 square feet. If you want to control individual rooms then the loops controlled by a zone valve would be only in that room. The loops combine in manifolds that are limited by the amount of water the circulator can move.
This is not a worry, because most manufacturers will desing the system for you on request. You can get more information at: