Don’t fast him as rabbits cannot vomit, there is no need. Make sure they are rabbit savvy… some antibiotics are toxic to rabbits and the risk of surgery goes up with a vet that isn’t experienced in rabbit care.
After surgery when he gets home, he’ll be sore and not want much to do with anything most likely. Be sure to request metacam (or other rabbit friendly pain killers) for him. Have fresh greens prepared, that is all my rabbit wants to eat after his neuter – make sure everything is easily accessible for him and take down platforms etc that would encourage him to jump until he’s healed up. Do a vinegar wash of his area to get rid of as many germs as you can before he comes home and keep it tidy to help keep away infection. Both my male and my female preferred a cool area (the a/c vents) after surgery, so maybe a cool tile or frozen water bottle available.
Check the area for infection (if he’ll eat you can get him to stand for a treat) daily until healed up.