I would start with a coop. The size will depend on how many you plan to get. I would get no less that 4 as they prefer large flocks, I started with 10. Personally I would get keets to watch them grow up and so they can get to know you a little better, plus they will grow up knowing that the coop is where to roost at night.
Keep in mind that guineafowl are loud and like to roam around rather than being caged. Once you get use to hearing their sounds, they really are cool birds that are relatively hardy and in my experience just as good as chickens when it comes to insect pest control.