I think the standard rule of thumb from Texas Hunter is 1 feeder per 10 acres of water. That said 1 feeder for 5-10 acres sounds like very isolated coverage. I'm on a smaller body of water than you are and went bank feeder only because I wanted ease of access to fill and much easier to seem them getting after the food (how long to feed at each cycle as it changes through the year).

Very pretty pond you have there.