Get a good mask and filter with it - it's worth the money. I've painted with PPG paints (automotive paints) on two remote control jets and used a HVLP gun and worked good. My paint booth was just some PVC pipes framed up with plastic on the sides - with a sheet on the floor and above. The amount of paint I was doing wasn't enough to consider putting in a fan. However, with your idea, what you could do is cut an opening for a box fan, put the fan there with a house filter taped on it so you don't get a bunch of paint going out - you'll be surprised by how much you catch. Just cut an opening the same size if not bigger and put a filter on it too.
Michael