A neuter is a small procedure surgery-wise. Most young boys bounce back in 24-48 h. There is always a risk with anesthesia, and that risk is there with all animals and with people too, not just bunnies. I don’t think you should be scared, but it’s only natural that you worry. He’s your darling and we worry about our darlings =) I was very worried when I had my Bam neutered.
Before surgery there’s not a lot you can do, feed him in the morning like you normally would, a bun should never be fasting. I think all other animals should be fasting prior to surgery except bunnies (and maybe horses, horses can’t vomit either).
There’s a bit more you can do when he comes home: Have a selection of his favorite vegs and treats on hand, give him an open water-bowl in stead of a bottle and if you have a hot water-bottle, you can wrap it in a towel and give him that to snuggle up to – but with enough space so he can move away from it if it gets too warm. See to it that he doesn’t climb or jump the next few days or for as long as your vet tells you to. Check his incisions daily, you can do that by having him meerkat for a treat.