For a pump filter, I am using a modified skippy filter. My pond thread is here....
https://www.backyardchickens.com/forum/viewtopic.php?id=146829&p=1
As for plants inside the pen, well, do you want stuff they can munch on or stuff that they wont eat for scenery?
I built my pen out of old restaurant racks, so I can't help on that front. With the amount of predators in your area, I would think hardware cloth.
Good score on the duck house.
I am the one who talked hubby in to getting our ducks. At first he thought I was nuts. Then he got a taste of duck...