The best way to introduce the flocks is do NOT house them together. Let the guineas have their own shelter, the chickens have their shelter, and they see each other when they are outside free ranging. They are most likely to do fine that way. Then the guineas are their own little flock, and they have their guinea flock dynamics, and the chickens are their own flock, with chicken flock dynamics. For the most part, they should ignore each other when they are outside and each do their own thing (this is what you want). The alternative, if guineas think that chickens are the same kind of bird as they are, the guineas will bully the chickens, and guineas can be MEAN to each other.
Other than that, my advice for letting the guineas out is pretty simple, just have them in some kind of pen where they can see outside, so they know a little bit about what the outside world looks like before they actually go out. Another trick that can work well is to let out only one guinea the first few days. They are very strongly flock animals, so the single animal let out will stick close to home & friends and come back in at night, but learn a little about the outside world so his/her friends can learn when you let them all out.
