I have the coop for bantams and love it, it would happily hold 8. However, my fatty pet rooster (a cochin/Brahma mix) probably couldn't fit through the upper door. Lol.
I have the coop you are considering. I love it - for bantam chickens - and will pick up a second one if I catch them on sale again. I have also owned ducks.
Yes, ducks will use a ramp (even my geese do) BUT the one that coop comes with is WAY to steep for a duck to navigate. Also the coop door...