The thermostat on the Remington Solar Attic Fan 30 - Watt is not adjustable.
It has a Humidistat and Thermostat that allow it to automatically fight moisture or heat based on its readings.
Yes. The Remington Solar Attic Fan (30 - Watt) will cover an attic space up to 2,500 square feet, so one fan would likely provide plenty of circulation for your 8x10 shed.