Pekins grow fast, so just watch them with the heat (panting and such). I think it would be similar to your pekin-muscovy mixes as far as brooding goes.
I know with my muscovies, they didn't get brooded by the book.
Muscovy won't fly until they get their flight feathers and then only for a short amount of time (for the males). Female muscovies can fly, but generally not far once they get older and they will stay close by their home. From what I have read, they just like to fly up high to perch (garages, trees, etc)
Mine are going on 10 weeks. They do have flight feathers and given the opportunity they might be able to fly. But, this is just a recent development. They are in their run so far and so haven't been given a chance yet. When that time comes, I am clipping at least one set of wings per duck.