10k for a single crew would be reasonably steady call volume wise, especially if the transport time is longer.
I work for a service that covers 25k ish with two or three ambulances. We have a chief and an administrative support person, and then all the rest of the non-clinical duties are divided between the field staff (15 of us). I do grant writing and social media, my partner does ambulance licensing, someone else does ordering, etc. I actually enjoy having some other things to do at work besides running calls since we aren't all that busy.