Architects may help you a lot, but structural design is for civil/structural engineers, especially in California.  6,000 sqft is a very limited piece of land to build a condo, but ultimately will depend on your specific zone and regulations (state, city, and county).  

You are doubling your transaction side exposure, adding far stricter license law regulations, stricter accounting regulations, billing & bidding approval processes & much much more.By all means give it a go but the age old phrase you don't know what you don't know looks like it's going to bite you in the butt here.

So while I am waiting for me to finish getting my **** together, I will get take REI off the side burner and catch up on regulations/laws, making connections/networking, research and drive for dollars to see if I can find houses for others. 

Title companies there shy away from double closings and favor assignments instead.My suggestion is that you talk to some title companies and make sure you can do a double closing or assignment wholesaling transaction first with them and also how they require (timeline and regulations) for your earnest deposit. 

****San Diego Short-Term Rental Owners and Managers: Tomorrow, Tuesday, April 9th, the California Assembly Judiciary Committee will consider Assembly Bill 1731, which seeks to regulate short-term rentals within the urbanized area or urban cluster of the coastal zone in San Diego County.

Make sure to check out regulation detail in New Orleans for Airbnb.

Whatever you do whether it’s wholesaling or one of the above strategies listed, learn the rules and regulations.

The ADU process is constantly getting more efficient but I suspect you will be unable to leverage these efficiencies.I question if your plan would be more productive on a SFR where you can leverage the state's ADU regulations. 

Local rules & regulations.

How are the vacation rental regulations?