just wondering how many builders wear a respirator when working with wet epoxy, wetting out, doing fillet work, etc ?

Warren-
I don't wear a respirator when working with epoxy. There's usually a decent 'breeze' in my garage shop - door cracked open,exhaust fan on low- one of the luxuries of working on the WestCoast. I am very careful (paranoid) about skin contact and go through a lot of gloves, use Tyvek sleeve protectors sometimes, etc. .
I generally use WEST epoxy, which is a lot less 'smelly' than some other brands - though that's no indication of potential hazard.
When sanding (anything) inside a kayak - like grinding out an old glass bulkhead - I wear a fresh-air supply mask. Otherwise I just crank up the ventilation in the shop. For most sanding these days I'm using a Mirka Ceros sander with a Mirka vacuum, and there's practically zero dust.
A lot of the epoxy/solvent/polyester/paint work I do in the garage under the house, I wouldn't do in the basement which shares air supply with the living areas.
I've walked through a couple of industrial boat shops years ago where I wouldn't want to work, but nowadays that situation is much better -I thank those 'health and safety/union/treehugger types for that!!