My concern would be how efficient these pumps would be and therefore your electric bill. Sometimes using something that is not designed for the purpose can be fraught with negatives. I pump my well 24/7 in summer for my trout pond and it's a 1 1/2 hp pump. It costs me about $100.00 per month in electricity. Fortunately I more than make up for that by selling the trout.

As far as the falls and pumping water out of the deepwater of the pondm I would be concerned that you will end up warming the pond in summer too much and have too warm of water for the trout.
I also don't think you will get much survial with their natural reproduction and what does hatch will probably be eaten but thier own parental stock. But I could be wrong. Not trying to be negative.
Both of you let us know how this works out.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.