When my cat was spayed it took less than a week to heal up. But it also depends on if the cat licks at the healing area or leaves it alone. Hope this helps.
I'd go ahead and wean them at this point... They're certainly old enough, and she doesn't need little teeth and claws on her belly right now. The surgery and recovery time is going to mess with her milk supply anyway, so might as well take the opportunity to get them off her.
No. You need to keep them off her, because it doesn't let her let go of the mating wants. The incision take a few weeks to heal, and it takes at least three-five months for the hair to finally grow back thick enough. I had the same problem with two of my cats, so good luck to you.