Just wanted to share our set up that works for us.
We have 23 guineas currently (9 female, 4 breeder males, and 10 free ranged males) in a mixed flock of 7 geese, 11 ducks, and 7 silkie chickens (downsized for winter, did have an extra 12 Juvie guineas, 5 adult guineas, 25 broiler & sex-link chickens, and 5 broiler turkeys) They all get along fine. Small fights have broken out a couple of times, but it's always with other guineas (when the dominate male losses a fight and they're deciding a new order) We have 1 really large pen (2 1/2 ft fence used to keep the geese from mindlessly wandering off our property while grazing), 2 large uncovered pens, 2 small uncovered pens, and 3 "chicken tractors" that we section off unruly birds as needed, but most of them "free range" (they hop from one pen to another when they want and will continue until we're able to afford getting them covered)
The pens are on 1/4 of an acre, we have 3 acres but the free rangers usually stick to the 1 acre next to the pens. The guineas ages are a mix of 1 & 2 years, ducks are 2 years 1 year & 2 months, geese are 1 y, Silkies are 5 months & 2 weeks (they are a family members pets).
The guineas have never been in the same pen as the silkies and we won't ever let them since the silkies are small, slow, stupid, look funny & can't see well through they're crests so I couldn't blame the guineas if they did do something. The guineas look through the fence but aren't really interested in them.
All of our birds are friendly, even our guineas. While most don't like getting caught, they'll come right up to us to see what we're doing and once caught they stay still and enjoy their pets (some of the guineas even make their "happy noises" when held)
Hope this post is helpful.