Question about exterior doors for a contractor?
Answers:
You may want to check with you municipality to see if they have a building code department. direct your question to them. these type codes vary greatly state to state. with out knowing the layout of your project it would be difficult to give you a good answer even without the fire and building code factor. You may also check with your home owners Ins co.: they may give you some in site to the question. good luck!
Other answers:
For your safety YES
For your safety YES
you need 2 doors. You don't need a gross negligence claim on you or your business.
If you are thinking about framing in an existing door, my advice would be don't yet. There is probably a good reason for it being there, i.e. isolated room or rooms with no proper egress. Check with the city and see if if you can put a egress window in, that would allow firemen to enter and exit with a person and equipment. Such a small place shouldn't be a problem to exit.
Check the local code. Some places only require an opening large enough to get out in an emergency and that can be a window.