The floating islands are a good idea. The roots of the plants go down into the water and create habitat for the fish too. I don't know about your particular situation, but in ponds they can be left in the water all year long.
We put 1/2 dozen of these in a customers pond a few years ago to help remove nutrients.
https://www.floatingislandinternational.com/All we had to do is add dirt and plants, then get some rope and we used cinderblocks for anchors.
The floating islands will work better than the lilies, which the boats can just drive through. I'd space the islands less than 10 feet apart to prevent the boats from driving between the islands.
