The answers to all your questions in the post are in the local codes.
The only exit to my office here in Renton is the front door. I have been to a lot of other offices whose only entry or exit is the front door.
The fire department comes to my office every few years to inspect it for fire hazards. No one has ever mentioned to me anything about another exit.
You can contact your city or county's building department. You may even be able to ask the fire department.
I would look at the local ordinances and fire codes first. Even asking the fire department might help you. If nothing else, they can direct you to where to look.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyze this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here