I've never been able to wrap my head around a windmill bottom diffused aeration system. My understanding is that you need to keep the pond turning over on a daily basis and wind is not very cooperative in that regard. Maybe I'm splitting hairs, but If I wanted to maximize my pond for swimming (or fish)...I would want something that I could rely on every day. If you have to stay green (very respectable), I'd advise solar with electric back up. This way the reliability is up to you, your budget and maintenance habits, not entirely mother nature.
If I were to use a windmill at my pond, it would be to pump some water for a little waterfall-like feature...cool, but not a part of the major health efforts of the pond. I'd love to hear the answers to your windmill questions and will keep an eye on your post. Windmills don't get a lot of thread-time here however.
Keep in the back of your mind that your small pond is a good candidate for a small electric diaphragm pump and a membrane diffuser or two. This would be a very affordable option with a small monthly electric bill.
