I didn't read all these in depth.
The closest pound to us is too far away, our vet won't give us a barn cat! IF they are spayed and declawed they only give to inside homes! But my barns are HUGE enclosed predator/dog free!! Congrats!
Make sure you don't feed him too much or else he'll get lazy. But if he likes you he'll bring you presents, mine used to bring me rabbit butts!
I put the new/old kittens litterbox right outside a hole in the barn door. We had an old cat that used to potty IN the barn, YUCK! So the new ones learned to go outside and we never had a problem.
Milo is a doll!!