With the variable speed control, you can set up a couple "walls" by using shower curtains. Side them out when needed and tied back against the wall(s) when not. This will help contain the over spray and allow the fan to move most of it out before it floats throughout the shop. The heavier the curtain the better and you can also weight the bottoms to keep them from getting pulled along with the draft. I have seen automotive spray booths set up this way and they work quite well at controlling over spray.
As mentioned, you should add filters not only to protect the motor but also so your not simply dumping the spent medium outside. And also, it is not a
big issue as of yet, but with the EPA's new NESHAP law concerning body shops (and thusly home auto body projects), it won't be long before any and all home spraying operations which atomize with pressure any type of VOC materials will become regulated too. At least rattle cans are safe!! For now!!!!!!