I have 4
To keep things simple.
I have one *main* vet, who I see for everything, both ferret and Rosey goes to her if she needs to. Although, she is only in on Monday, Wednesday and Thursday.
I have another vet I will see at that same office, who I go to if the main vet is not there or is swamped, and it is an emergency and needs to be seen that day. I am not even sure of her schedule, I have never had an issue where neither were there.
I have 2 other vets at another office, that is about 10 mins further away walking, in case I absolutely cannot get in with the closer ones, or if it is something that needs more than that office can do.
Then I have the vet at the emergency clinic, who I feel comfortable seeing if need be.
ETA: I guess that is actually 5...