Sounds an amazing place! Some pics when you have finished would be welcomed.
Worst case scenario. Fan, the trouble is that whilst it may seem always windy, sods law says that on the hottest days when you need the wind it will stop and it doesn't take long to fry plants
so I think a windmill would be risky.
At least with the sun, no sun = no heat. You are guaranteed power for the fans without any fancy control circuitry. Yes computer fans are popular and cheap. It might be good to have at least 2 on separate circuits and solar panels in case of failure. A simple protection device for the fans would be a suitably power rated 12volt zener diode. This will stop your fan getting extra voltage and which would reduce their life expectancy or completely burn them out. Hope this helps.