You can get you a 120 V PC fan already has a regular plug on it. Kinda loud but pushes a lot of air for its size. 60-70 CFM. I've had it for years so probably something better out there.
http://us.100y.com.tw/chanpin.asp?MNo=53540
Odor control I use an O3 generator. Study up, they work great but you have to size the room and not overload a living space with O3. You use it outside the cab to clean the air in the closet.
A 4 inch probably isn't major overkill tho. If you get like an inline fan or something with rated CFM to your space. I mean, I really don't think a 4 inch is overkill at all to tell you the truth. Just don't get something mega powerful.