I have a pen. I use on my young breeders. They do not free range until I get my 500 eggs from them. It is 50x50 or 50x60 something like that, Huge pen. I have the net 15ft high in the middle. I have an attached coop out of wire and plastic with high roosts 10-12 feet up. The building is 20x10 and 16 feet high.
I have cross bars on the posts holding the netting up about 3 ft from the netting. The birds stay in this pen about 8 months before they get freed. I lose a few even in the pen to owls, they will hit the net hard and fast and it stretches to the point the owl gets the head of the guinea.
I really wish you luck, you sound determined to make it work. That is a good thing. Be flexible and adjust as need be. The Guineas will return to their coop at night for me. most the time. However, there are nights they refuse to go inside. Full moons are the worst. Just get extra birds knowing some will die.
Good luck!
Of course. Thank you for your advice!