I'll share my experience raising
chickens and guineas together. i didn't have problems with them housed together in the evenings, or at least not for the most part. I'd do my space considerations for roosting/night housing the same for guineas as standard size chickens. For space on the roost, give them 8-10 inches for spacing/bird. Guineas can probably go with 8 inches of roosting bar space. I don't know your climate/environment, but assuming you plan to have them outdoors with plenty of room year round, they need less confined housing space. I'd go with a very, very minimum of 4 sq. ft./bird for confined housing for night time predator protection. If you think they'll be in more often and have to be up indoors more often, give them more space, like 10 sq. ft. or more if you can. The more space, the better.
Now to my experience with a very similar setup to what you describe:
t started raising fowl with 4 chicks + 4 keets (baby guinea fowl). I raised them all together and held them a fair amount when they were feathering out. I also moved all of them into the
chicken tractor together. They all were on pasture in the daytime, and put up in the chicken
tractor at night. By raising and training the chickens and guineas together, I found my guineas easily came up to roost in the chicken tractor. Of the 4 keets, only 1 was female. However, that female generally laid in the chicken tractor. She didn't necessarily lay in the nest box, but she would lay in the tractor and then go back out and free range. Maybe I just got lucky. She only was around about 1 year. When the fall came, I guess she was looking for places to have babies, wandered over to the neighbor's place, where she mat the neighbor's dog. The end.
To the raising of roosters and male guineas together, in my experience, I wouldn't do it in that small of a flock. I had ordered 4 pullets and 4 straight-run keets. 3 of the 4 keets ended up being male. The male guinea fowl seemed to work out a "rank and file" type of order and didn't go after each other the way roosters would if 3 were together in a small flock. However, one of my pullets turned out to be a surprise rooster. The whole flock of 8 got along swimmingly until puberty struck. Then, those 3 male guineas chased the cockerel mercilessly. If they caught him, they pecked him, etc. They took out his beautiful tail feathers, etc. They bloodied his comb at times. We tried different strategies to change that behavior, like putting a large plant pot in the chicken tractor so the rooster could hide behind it. It didn't help. We didn't have separate poultry housing and felt like those guineas would eventually run the rooster ragged or kill him. We rehomed the rooster to another family in the country.
I hear of people having guineas loose and how they will roost in the trees...and I also hear of how one by one they disappear b/c of predators. Others may have different experiences, but that is a common story I've heard told from people with some
land who raised guineas and let them roost on their own. I think it's wise to have them go up in the coop with the chickens if you want to keep them as part of the flock.
Multiple poultry flocks later, I still have 2 of those original 4 guineas (they are tough birds!). We actually let those 2 guineas generally be cooped up on their own and join the hens in being on pasture in the daytime. While they do well on pasture with our hens (which are not the original flock the guineas were raised with), they are a bit tougher on some chickens than others. Sometimes we house them together for specific needs,but when we do, we make sure the coop space is oversized for those days we may not let everyone out on pasture.