new pd's with outside cage..????????

Getting 4, three month old pd's tomorrow. I have built a 16'x8' enclosure outside with 3 1/2' walls with metal to keep from climbing. It has black, flexible, 4'' pipe on the ground that has two openings that go to four different hidey houses, all under the dirt, and all inter connected for air. The floor has small welded wire that connects to the walls, which covers the ground to prevent digging. I hope they adopt the burrows and build mounds around the entrances. they are supposed to be tame and I was wondering when I feed them outside, do I free choice feed or do it on a schedule with portions???? any info on this whole set up is wanted and needed. I'm new to the prairie dog and have been reading everything I can on them. I am sooooo excited and have always love these little guys. thanks, Laura