I voted for 4, though its usually way more.
Aside from taking the dogs there to get their shots, we have to take Frisk & Ethan there to get their nails clipped every so often.
The cats only go once a year, though. Just for shots.
None of the other animals go unless its an emergency. The only non-canine, non-feline that has been to the vet this year was Otto(one of the rats) to get an abcess removed.