[KevHw]

It'd help if you maybe post a diagram of your plan. Could give us a better idea about what your talking about and help us offer better suggestions.

Personally, I'd use computer fans to prevent paint destroying the vacuum cleaner. Of course if you can, use a filter infront of the holes, inwhich case it doesn't matter if you use fans or vacuum. Get some nice big fans, (smaller than 8cm diameter won't be too good) and mount them 1/2-3/4 way up from bottom of box. I had a very make-shift "booth" with a high powered fan on the side which worked ok. I'd probably have them behind though, or towards the sides of the box. Most spray booths (or at least large scale ones) have the extractor fan above the spraying area.

In my mind, the important functions are to create a steady flow of air, fast enough to carry dust and paint over-spray to an exhaust outlet, without dragging the dust onto the freshly painted body.