UPDATE***
We recently enlarged the pond to about an acre and a half.
With all of the water you have available I would make the pond as big as possible. A bigger pond is going to make a better fishery. I don't know if you have more room for expansion, but bigger is better up to a certain point.
Think about your forage production just like you do your gamefish. If you put a lot of time and effort into making spawning structure, cover, feeding areas, and area where forage can live and grow, you will do your pond a HUGE favor.
