Does this turn on and off automatically when heat or humidity is needed or not needed?

It turns off and on based on parameters you specify

Would this work to control a fan in order to keep humidity down in a garage?

Yes, it can. Please use it within 10A(current).

What’s the difference between this and the itc 608? is the 608 a streamlined version of this (which is 2 products)?

Hi, thanks for asking. The difference between these two version are as following. 1. ITC-608T supports a maximum output load of 1800W. 2. ITC-608T has two plugs for devices while this 308+200 supports 4 plugs, two for heating/cooling, two plugs for Humidification/dehumidification. 3. ITC-608T supports "time stage periods for temp control mode" - so you can program it to ramp the temperature up and/or down.

Would this be proper to use is converting a refrigerator into an egg incubator?

Hi, thanks for asking. Please contact us with more details with the egg incubator, we will try our best to help you. Contact us: 1. Inkbird home page: https://www.amazon.com/sp?_encoding=UTF8&asin=&isAmazonFulfilled=1&isCBA=&marketplaceID=ATVPDKIKX0DER&orderID=&seller=A1RUFFFCQ74BCW&tab=&vasStoreID= Click "ask a question"on the top right to reach us. 2.Email: support@ink-bird.com