Tracy, I went with 1/4 acre pond, max 8 foot depth, as grow out water for my main BOW, a 7 acre pond. Like you, I intend to pump water in it, but fortunately it is close enough to main BOW to simply drain the contents into it when desired.
Based on what Bob Lusk said, this is about right size for what I want to do, which is raise CNBG or tilapia to feed LMB in main pond. I went a little deep to minimize losses to cormorants, herons, raccoons, etc.
Bob did tell me that there is an inherent difficulty here: BG spawn best in 2 feet or less, but this shallow means weed problems. Still haven't figured that one out, guess I'll put down landscape cloth then pebbles to reduce vegetation.
