For our ADU (garage conversion), I am handling the design/engineering and then selecting a final contractor once its permitted and ready to go. 

@Kate Zieverink McMinn we just hosted a webinar with a friend in Orange County, CA that used to be a public works engineer.

You may have to search a bit for the right contractor or engineer - sometimes I see one solution dominating in an area - "that is how we always do it" 

I can search it but same deal, the search engines don't evaluate the results.

Most of our clients are professionals - physicians, attorneys, software engineers.

However having developed many subdivisions myself I was able to work with my client ( who is a very experienced civil engineer that did projects in NYC) So determined that with the base zoning it was not a matter of if it was how many and how  long to get approved.this is probably one of the top 10 markets in the entire US for new builds you would not have Toll brothers there if it was not.  35 minutes or so West of Dulles and all the high tech in that area..

I am an engineer who works out of his basement everyday and rarely is on the phone.

Work with your attorney for what is needed to insure all subcontractors get paid by the General Contractor.Make sure the insurance covers Construction period and also materials.Talk with your Commerical insurance agent and they should address the above questions with you.If this is an older facility make sure your engineering firm has covered Fire Suppression systems and any Storm pond or drainage systems. 

Quote from @Jeremy Dugan: I am a US Air Force and Massachusetts Air National Guard veteran with 20-years of experience as a military Civil Engineer.

He is an engineer and pretty risk averse.