We need to get Poconos or one of the other experts on pump motors to look at this. They may be able to save you serious money.

As for sizing there's what's called "upRated" and "fullrated" pumps and 1/2 h from Full rated means more flow. But the real key is figuring how many gallons per minute it will flow, what the filter can handle, and how long you have to run the pump. For maintenance mode, I cannot see 1/2 hp not being sufficient. But for other tasks? I'm not sure.

Carl