Are they dedicated circuits or do you have other stuff running on them? If they are at least 15amp circuits and fairly empty I would think you'd be OK. A standard cheapy power strip is rated at 15amps and 1800+ watts.
That being said, it's your ass on the line not mine. Take electrical...
I would think a 250cfm fan would do the trick. If you are worried about it buy the next biggest fan and use a fan speed controller. Actually buy a fan speed controller anyway because it's nice to be able to control the output of your fan. A larger carbon filter will work with a smaller fan...