Yea you can do that. the size of the fuse depends on the size of the wire. 14/2 with a ground would be 15 amp fuse or breaker. 12/2 with ground would be a 20 amp. you might not want to slow it down at all, those small fans don't push much air iwhen a static pressure builds up. just make sure that when the fan is on thereis pleny of air being vented in.

OH, and welcome to the world of growing. the best thing I could tell you is be patient.