Not too long at all. There was a BYC member here who's hen flew over the run for somewhere around 8 hours. She got her back in and she went back to setting on the eggs, and all of them hatched. So don't worry, they'll be fine.
Sounds like things are going well!
Broodies don't lay. They don't eat much, so they are conserving their energy for hatching. Yes, she will turn the eggs.
A BR should be able to cover all the eggs if you want her to.
As for the other chickens bothering her and the chicks, I don't know. Some people separate the broody, some don't. I suppose you won't know until they hatch.
I haven't had a broody yet, but I've read loads on it hoping for one.
I'd give her a couple more eggs (tomorrow will be fine, they're in the incubator so they'll all be at the same point in incubation). If they end up with blood rings or quit for whatever reason, you don't want to end up with...
Sounds like you might have a broody. Is she on the nest at night? Once she stays on the nest at night, I'd slip her some of the eggs from your bator. (assuming they're not super close to hatch)