I am waiting to get paid next week, then I plan to buy a 15W solar panel and a 15 watt dc pump. The pump I have chosen is the Sun-15 from Sun-Pump. The few reviews I have found have been positive, and the pump has a maximum head height of 9'11", which will work perfectly with my idea for a solar collector.
So far the search for a 4" fan has been tough. I want a fan that draws between 5 and 10 watts, which is proving to be difficult. The search continues.