roselvaggio's point is the one I would build on, because there is a number behind it.
A field tech adds capacity but also adds a schedule to manage, invoices to track and another line of customer communication. If the admin side is already where things fall through, the second tech makes the pile bigger, not smaller. You end up paying for capacity you cannot dispatch cleanly.
The part that usually decides it: what is an hour of your own time worth in the field versus at the desk at 9 PM? If you bill $150 an hour on a truck and you are doing three hours a night of admin, that admin is costing you more than the office hire would, and it is costing it in the least visible way possible because it never shows up on a P&L.
HUGEHomePros is right that hiring office people eats time. That is real, and it is the actual reason most owners keep putting it off rather than the salary. Whatever you decide, budget for the hiring process taking longer than the job posting suggests. I recruit for these office seats for a living, so weigh that, but the sequencing question is the same no matter who you hire through.
