A graphic designer will keep your standard of work high, but find one that's also willing to assist with customer contact. Instead of handing the job back to the receptionist for proofs, have them deal direct with the customer so that changes aren't "lost in transit". A system like Signvox can save a lot of time here.
My staff mix is:
1 General Manager (myself, mainly doing quotes for the sales people and covering anywhere required)
1 Operations Manager (signwriter & tinter, does scheduling, customer contact, covering anywhere required)
2 Sales People (on the road)
1 Receptionist/Admin
1 Accounts (offsite)
2 Graphic Designers (one works remotely)
1 Window Tinter
3 Production Staff (all signwriters, also assist with installation when required)
1 Installer/Fabricator (qualified builder)
I feel like that's a pretty balanced staff mix for the general signwriting that we do. Next would probably be an in-store salesperson/extra admin.