We have some contractors and some surveyors and some architects in my area that often go through the zoning process for clients in my area.

My land is also buildable and I have plans from an architect for a 3 bd/2 ba home which would cost 300k to build (it's in CA) and is in an excellent STR location...but I'd need a construction loan to build it.

Should I hire an architect and GC before even having anything laid out and use them as resources?

In this case, you should have an Architect / GC visit the space and tell you what it would take to make the basement "legal".

Architect & Engineering plans Rendering Surgery 1 & 2 County permits Municipality Utilities District costThese are the permits I am aware of, but I know there has to be more permits I could be missing. 

Similar I had jurisdiction architect approve a sheer wall to ceiling but inspector required it to go to shingles.

Feasibility study is done, we have been in contact with architects and GCs and are currently working with the town to iron out all the permits etc.  

Any recommendations for cold calling lists for either Wholesaling, or retail selling ( I am a realtor / flipper / associate architect).

Right now we are in the process of working with our architect to design the layout.

@Matthew Gentile if you are trying to be an architect, engineer, attorney, etc additional education is helpful.