Ask them about everything. They might ask to take a blood test first to make sure they will take the anesthesia safely. If they dont ask, you can always request it (i recommend asking for the blood test first). Ask how often the vet has failed (never go to a vet who has a fail chance of 1%+ on a neuter). Let them know you need specifics on how to care for you bunny afterwards as some vets will print up an after care sheet

I want to note as well that not all vets will neuter rabbits until they are closer to about six months old. The younger the rabbit, the more likely they are to hide their testicles inside of themselves which can make the surgery a little harder to do. Is there a reason you need your little boy neutered so early?