I would maybe start a little slower than you are planning to. Only let one guinea out the first couple days. One won't wander too far, and will come back in to roost at night. Then do two, etc., as you have planned. I personally like when they come back in to roost at night, I know they are safe. I know you have different goals for your guinea flock, however they may adjust to outdoor life a bit easier if they only have to figure out the free ranging during the day first, and then can figure out roosting outside at night later. Guineas adapt to roosting outside very well, mine always seem to just decide, "okay, we aren't going in that coop anymore" and one night, everyone is out. (Of course, that's the night it's going to storm, so I have to chase them in anyways...)