From my experiences...it depends on your rabbits and your colony setup.
If the buck is left in with the group all the time, the does WILL, eventually, stop the instant rebreeding. (there will always be some that are doormats, tho). In order for this to work, the colony needs to be a fairly large size so the doe can not only get nasty at him, but run away, or into a hidey hole (like undergroung) In the meantime, they will get rebred every time they kindle.
I think it's probably a 75/25 deal on whether the buck will interfere with the kits. Other does will interfere sometimes, as well. Again..depends on if they're used to each other, have established respect, and if the colony is large enough for each to have their own section if necessary.
As to how long to let them nurse...My kits nurse a LOT for around 3 weeks, then occasionally at least 10 weeks. I don't wean, the does do it unless I've sold someone (I don't sell before 10 weeks). The kits will nurse as long as the doe lets them.
Allowing the doe to determine when to wean means the kits are introduced to pellets/grains/whatever you feed naturally...at their rate of growth..not in an artificially determined schedule. Weaning enteritis is virtually unheard of when you allow the kits to continue to nurse until mom weans them.
My schedule now is to leave the buck in with the does for 3+ weeks, then remove him to a pen next door. After the kits are out hopping around and eating pellets/drinking water, I'll put buck back in..IF I want more kits right away.
I do have one doe who lives with her buck full time. He's an excellent gentleman, and never interferes with the kits or kindling. The doe is a very assertive girl, and doesn't let him rebreed her until a few weeks after kindling.
Oh...if you DO leave the buck in the colony, and you are getting rebreeds every time a doe kindles, you'll find that the does start to have fewer kits each time...they seem to be able to adjust how many kits they have at one time if they're continuously rebred immediately. I've no clue HOW it happens, but there are others who've researched it and found that the does will only use 1 horn at a time if they're being rebred every 30 days.