Good luck. I too am a civil engineer with about the same amount of experience...so I am interested to see how this works out for you.
I think there may be some federal tax benefit to being a sole proprietorship...but a CPA would know for sure.
Some of the smaller firms that have started where I live office close to a printing shop...so they can use them as an extension of their business - all printing, electronic plan room, large sheet scanning, even plotting progress sheets if you can’t afford a plotter right away.
Some cities have ‘business incubators’ where you can utilize an admin person, voice mail system, etc on the cheap.
I think one of the larger expenses could be professional liability insurance...so it may be worth investigating the minimum level required by your prospective clients, and shop around for a rate, before making the ‘leap’.
Sounds exciting.
The business incubator idea is a good one. There was an article about one of them in a recent Chamber of Commerce newsletter in my town.