Hmmm - well I would say your body is pretty used to it all, so in my eyes you would be able to do it for a few more weeks. I kept umpiring netball til 20w this pregnancy, and last pregnancy I played netball to 19w.
Also last pregnancy we renovated a house, and I was up there on the ladder with the orbital sander, so I'm no stranger to fumes, machinery and that kinda jazz.
I guess at the end of the day though - if you are asking these questions then maybe its too much for you? How would you feel if god forbid something did happen as a result of it all? Could you ever forgive yourself?

I get heaps of BH's too - like loads and loads, and always when I have been doing too much - well not too much, but some rigourous exercise of sorts. So I get where you are coming from re irritable uterus. But if you think its over, then really its over. Start settling down and give yourself a bit of a break.
The business will cope one way or another, but how about your emotional state?

BTW - I hate vacuuming too, I'd rather mow our lawn or wash our car then vacuum as it really sets me off!!