First, you are monster.
Second, houses, ponds, and property are AMAZING....
20x20x6' = Appox. 27,000 gals.
I would think a pair of Pimas would be fine in there plus a supply of feeders for extended stays elsewhere.
You are on the right track with re-hab of the pond closest to the deck first. That is where the parties are

and best viewing spot for fish. Also, with added filtration in the form of a waterfall or similar, the sounds of the pond will be enjoyed fron the deck and house.
It looks like the Water lettuce is contained in a filtration/gravity type trough. Can that be made larger, or is that already in the plans?
Maybe a similar type system can be retro-fitted to the other ponds with poor clarity. The trough design will act as a settling chamber and have floating plants which will also collect silt and improve clarity. The chamber could be flushed when you visit. Then electricy isssues arise... would hate to see you invest in some fish that would only see flashes of them from time to time. I guess flooding issues would be a concern in the larger other ponds when exotic species are stocked?
Many options for filtration and housing and I'm glad you are taking your time you lucky SOB....