Yes having the drainage as a horse or cow pasture may well effect fertility of the pond. You may not need a fertilizer program at all. All the more reason to get the soil tested and keep it well limed. Go slow on the fertilizer (as in don't) until you get the soil tests and you know how the pond will do without it. It may need to have some added but watch your bloom first.

I can't say much about windmills. There are a number of very good discussions here about them. One key for DO (dissolved oxygen) purposes is do you have enough wind at the right time (summer nights in the south). Here is a link which contains several links to other windmill threads.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=11;t=000176