Should a Growing Business Hire Office Staff or a Field Tech First?

One thing to think about - hiring office people takes a lot of time and you won't be able to work in the field while you are doing it. I think the move is to replace yourself where you are at now, which is in the field. That's the place you have to get out of asap anyway. Find someone you can coach on how to do things your way. If you need someone to answer phones, you can pay a service in the meantime to at least pick up the calls until you can have the time to train someone on how to do it.