Hi Rich,
RO/DI units like back pressure we all know that. I think 175ft of drain (waste water) might be pushing it. Can you explain more about how the pipe will run. Also what diameter it is? Its a good idea to use the waste water. Have you designed your pond to take large amounts of water. Does it have a run off itself?
Re. the chiller, my concern is not the distance it'll be fine with that (mines about 35ft one way. I'd worry about flow. Your chiller will require quite a sizable pump to drive the water through the chiller. Most chillers need about +-500Gallons an hour. Have you thought about using your main pump to drive the water through the chiller and then upto the tank. I did it this way and it works great. Also you need one less pump.
I want to look further at your design. I cant remember now if you included lighting. If not can you explain what you are going to be implementing.