Incubator fan question

Does it matter how hard the fan blows? Im going to buy a fan with a usb cord because I have a usb wall charger and I can just plug the fan usb into that and the wall charger into a dimmer to control the speed. But does the speed of the fan really matter in an incubator?

Not really no as long as your moving air pretty much any fan will work.

I would use at least two, one blowing up from the bottom and one blowing down from the top. As far as speed goes the one you mentioned sounds perfect. What you don't want is the one that the original refrigerator came with ( too many vibrations).