Sounds like you've got a set-up similar to mine in the garage manglord. That's exactly what I use, but modified some for use specifically for pressure casting. Same deal though (paint pot with large professional compressor for auto repair, nail guns... you name it).
It's basically more efficient, and I can do increidbly large castings by comparison to my little pressure cooker set-up in the house. I use that in the winter a lot though, as casting supplies don't do well to fluctuating temperatures in the garage, and sometimes I just don't like the cold. And since more often than not my castings are smaller (for figures, weapons, etc.), I can usually put off any large part castings till the Spring and Summer anyway.
Good luck... And I wouldn't worry too much. I have safety valves on my equipment and likely you do too... But do be careful. I do know someone who blue his hand (whole hand) off with a blown paint pot.