Guineas are a true blast, so entertaining and fun to watch but very independent, active and flighty. I personally love them and got them first, then chicken math took over. Lol.
I have my guineas and chickens cooped up together and in the same runs and haven’t had any problems. They sleep on the same roost bars too. They really just ignore each other, it’s kinda funny to watch them dance around the other. They don’t peck, chase or fight with the opposite bird, only their own kind. Except momma hens, both guinea and chicken, will peck at anything that disturbs their babies, even other babies. 
A big difference is that guineas do not like confinement At All, dawn comes and they are at the door pacing to be let out. The chickens are content to wake up slow and laze about the coop and run, they’ll even happily scratch (aka excavate 


) around in the coop if you use the deep litter method. Guineas are MUCH more active and they don’t scratch around nearly the same, they “need“ to free range and stay in motion. Which is great as they eat all the bugs, don’t destroy your garden and are a great alert system. Mine watch the sky constantly. They can be crazy loud when they are scared or alarmed but that’s what you want and they quickly quiet down once the threat is gone. I personally find them more alert even than my roosters. 
I have chicken hens that loudly croak all day long, they are the real noisy ones. Lol.