Small fleets are the common case
Most businesses that walk into a store like this are not running fifty trucks. They are running three vans, or a pickup and a trailer, or a handful of vehicles that somebody keeps track of in their head.
Fleet services is worth asking about well before that gets difficult. There is no minimum, and what it adds is consistency: the same tires fitted every time, work scheduled rather than reactive, and a record of what went where. The point it starts paying is usually the point at which nobody can remember what is on the second van.

