My thought initially was 50 fish in that size is probably do-able if that's all. But, when you say a breeding stock, with that, you instantly lose control over what other amounts are in the pond. I don't see any way for you to control that in a good way.
Also, I don't think your rainfall amounts would be enough. I think you would want a "regular" flow going in, and preferably some out.
Unless the plan/situation changes, I would agree with FireisHot, and snrub.
