I have no experience with runners but maybe this can help anyways. We have a completely mixed flock. 7 different breeds of chickens (1 of each all different sizes), 3 Rouens, 2 Muscovys, and 1 Pekin. Ours all live together in a large pen. Currently 5 chickens have a house all alone, the Rouens and the Pekin have a house, and 2 chickens (bantams) and 2 Muscovys share a house. At then end of this week they will all be living in the same house together. The 4 ducks sleep on the floor but the Muscovys like to perch sometimes to sleep. Luckily for us we have all girls. I have read the drakes can be kind of aggressive with their mating so this would be the only thing I would think you might have problems with.
I would not add ducklings into the flock until they have some size on them and can defend themselves against the others. Chickens and ducks can go after babies, killing them. If you have a broody that will take the babies under her wings then she will protect them. I can tell you that it seems, with our flock at least, it took the ducks a lot longer to be accepting of new additions than it did the chickens. Ducks by nature seem (to me) to be very nervous of new things and slow to adjust, but there are always exceptions to the rules...
