I don't know about ducks, you can ask someone on the duck threads at "Other Backyard Poultry," forum above.
As for chickens it is 4-5 sq.feet per bird not including roosts, or nest boxes. and 10- sg.feet per bird in the outdoor run. If chickens are too crowded they resort to fighting, feather plucking and even cannibalism.
Your coop is 8 x 4 so 32 sq.feet - so at most you can have 8 chickens- it would be better to have one less less. Height is not important , chickens spend most of the time on the ground or floor. You have 70 sq.feet of run space,= 7 chickens.
If you live in an area with severe winters where chickens will stay inside the coop for days at a time, it's better to allow 5 sg.feet per bird in the coop. Hope this helps you out.