These are really questions you should be asking the vet
before the spay so that you know if your vet is rabbit savvy or not, as getting the wrong answer from them might mean you should be finding a better rabbit vet for the surgery.
Questions to ask the vet are: if you will be sent home with pain meds, which one, and how many days worth. If they don't say they send several days worth of pain meds(usually meloxicam/metacam) home with you I would suggest finding a more rabbit savvy vet who knows that rabbits
need to be sent home with pain meds. Ask if you need to fast your rabbit the night before the spay. If the vet says yes,
find a different vet as this one is not rabbit savvy. The vet should also tell you how long to keep your bun on restricted activity. This should be 1-2 weeks of no running or jumping, as a spay is an invasive surgery and you don't want to risk injury to the incision.
You will likely get the answers to these questions from the receptionist. Sometimes they are not well informed, so if they answer any of these questions wrong, ask the receptionist to confirm these things directly with the vet. If the vet confirms that you will not receive several days of take home pain meds or that you should fast your rabbit,
find a different vet. Any good rabbit vet should know that rabbits need pain medication as rabbits in pain are less likely to want to eat, and that you should never fast a rabbit prior to surgery as rabbits can't vomit and it's also essential to keep their digestive tract moving by continuing to feed them, to help prevent GI stasis setting in.
As for eating after the surgery, a rabbit should be eating well by the next morning, if not then syringe feeding may be necessary. But again, this is something your vet should go over with you either before or after the surgery.
A few other things that can make the surgery and outcome as safe as possible for your bun, though it will also increase the costs of the surgery. Have blood work done prior to the spay to ensure your bun doesn't have any kidney or liver problems, and doesn't have an underlying infection. Make sure your vet intubates for the surgery. This ensures a secure airway during the surgery. Not always necessary, but I did have one rabbit that would have died without this being done. Check or request that your bun has an IV set up for the surgery. This means your bun will have IV fluids and will also be able to more easily receive life saving meds if anything does go wrong. Also having the best and most experienced rabbit vet in your area performing the surgery. None of these things are absolutely necessary for a successful spay for a normal healthy rabbit, but there are always the rare few instances where having these things done can save the life of the rabbit if there does happen to be a problem. But like I said, it will drive up the cost, probably by a few hundred dollars unless it is already included in the current price you were quoted.
You may also want to take a look at this link, as it has some good pre and post spay/neuter info.
http://www.bio.miami.edu/hare/opcare.html