Hi Mimi13.
We have a pond around 700 gallons, a submerged pump, and large filter with bio balls and sponges. I can't remember the rating, probably a few thousand gallons.
Our issue was I had waited too long to clean the filter. It filled up with with stinky brown sludge and really overwhelmed me. The pipes also filled up with the sludge and it began dripping out of the fountain head.
Overall, I like the pond. I kept it. But the filter needs to be pretty powerful (at least triple the pond volume per hour) and it really needs to be cleaned out at least once a month, probably every two-weeks. The benefit of more frequent cleanings is that it is less gross/sludge per cleaning, quicker to clean the filter, and a healthier pond.
Our filter has a mesh bag around it. This bag helps keep it from getting clogged, but the suction pulls in the bag. So every day we have to pull the bag out. A firmer type of "cage" like object around the filter might be easier. Also, getting a pool cleaner, I don't know the name, a long stick with a net on the end - would probably be useful for cleaning out feathers and things that fall in the pond.
We only have four ducks. This winter, we live in Michigan and the pond freezes, so we emptied the pond and will try again in the Spring.
I honestly don't know if it needs to be cleaned out COMPLETELY every few months or if you will need more filtering plants at the bottom.
I hope this was helpful. Overall, probably worth it because you don't have to dump it out every day which helps save water. Although, cleaning it out takes water. It's also stinky if you can't clean it out properly. It is just taking thought and adjustment. The ducks swim in it for hours a day, so it's probably worth it.