I don’t know what can be done to solve contamination issues, but I do know that gloves, a lab coat, and a mask aren’t necessary. That doesn’t prove they’re not helpful in a marginal way, but I and probably a lot of other people have managed large numbers of plates with minimal contamination issues without them.
The main things are pretty obvious: keep your plate area clean, and don’t leave old contaminated plates next to newer clean ones. If you’re having problems with mites, get rid of any plates that might have them (or at least move them elsewhere), clean thoroughly, and use flame: ethanol doesn’t bother mites (I don’t know about low bleach concentrations). Seal up cracks in and near the bench where mites might be living. There are a couple of things that can dissuade or stop mites: they apparently can’t traverse a film of mineral oil (they either avoid it or get stuck, I’m not clear), although that makes a terrible mess, and they don’t seem to like traveling on exposed metal and can’t burrow through it like they can parafilm, so you can lay down aluminum foil to deter them (you can also flame aluminum foil) and can wrap plates in aluminum foil before placing them in contaminated incubators.
Regarding sources of contamination beyond your immediate benchtop, I don’t know what you can do. Obviously, you can try to control mess and dust over your bench, but only to an extent. It is however my experience from having less fastidious baymates or even having some of my own old plates lying around that even the visually dirtiest plates are not a significant source of mold infection beyond a couple of feet (laterally - downward from shelves might be a different matter).
Regarding using a hood, I’d be a bit worried about the higher flow rate. I’d be especially worried it would tend to rapidly dry plates left in the hood, but even while picking I could see it being a problem, as it might make fungus spores travel more easily.
A couple of more points:
“bleaching the worm” usually means dissolving worms in bleach (where “bleach” means various compositions of sodium or potassium hydroxide and sodium hypochlorite) to recover their eggs. It is often the only way to eliminate bacterial or yeast contamination. Completely dissolving the mothers is not usually necessary to eliminate fungus: you can mark the spot on the plate onto which you transfer worms from a fungus-infected plates, and after the worms move away kill everything at that spot with strong sodium hydroxide or other “bleach”.
If you have minor fungus contamination and spot it early, you may be able to kill it by direct application of a few microliters of “bleach” without harming the worm (elsewhere on the plate). This isn’t usually best practice or even successful in the longer term, though.