Just an FYI on hoods, we use several diff types in Pharma, depending on the purpose. Traditional fume hoods (ie chemical hoods) are a designed to prevent exposure if the operator to fumes by having a sash a the front for air intake, and a number of vents at the back (at bottom, middle and top) to pull off the nasties.
Microbiology labs use Biological Safety Cabinets; same general front and back to them, but an added channel of out-vents right inside the front lip of the hood, so that anything floating in through the operator's sash gets sucked out immediately and can't contaminate the plates.
The third type I've seen are Laminar flow hoods. These are used in Sterile Manufacturing, and work in reverse from most fume hoods - thy have a hepa-filtered fan on the top of the hood blowing air in, and the air blows out over the operator. This works to prevent contaminants from approaching the clean surface.
To maintain aseptic conditions, you'd probably be wanting the third type, rather than the first. How you'd DIY that I don't know; I get to buy all mine from suppliers...