Also keep in mind, just because a property already has a pond, does not automatically disqualify it for a second one.

Why not go for the best of both worlds? Buy a property that has an existing "ok" pond to fish and mess around with but also has a good site for your dream pond. You have a pond to fish and experiment with while you are building the pond you really want. Then the "old" pond can be a trash fish pond (to put all the fish you cull out of your dream pond), a forage pond, a kids pond............. etc. Whatever you want to make of it.
Several years from planning stage to good fishing in a new pond. That is if nothing goes wrong in the process. Just a thought.