California 2020: Duplex vs. ADU

[Bradford Mills]

I am looking to convert a single family home (SFH) into either a duplex or an ADU. This is my first house, first duplex, first purchase using the VA loan. I need help identifying the pros and cons of each strategy, ADU or duplex route. The home doesn't need significant renovations in order to make two seperate, but attached units. All I need to do is put a wall where a door is and install a kitchenette. This will create a 3/2 attached to a 1/1 with a sunroom (where I will install the kitchenette). I plan to keep the house for a long period of time and rent out both units in the home once I have met my 1 year minimum occupancy time required by the VA loan. Below I will list out all the considerations for this situation...

1. Zoning: the home is in Vista, CA in an office professional (OP) zoning district. Right off the bat, I am not sure if this zone allows for multi family homes. I've tried calling the Vista Building Division, but haven't learned much. If it is not allowed, how painful is the process of getting it re-zoned to allow for multi family? 

2. Code requirements for a duplex: I know I need a fire barrier on all the walls that are shared by the two units. I need noise insulation. I need parking for both units and seperate entrances to the homes. What else am I missing? What I don't know about is getting separate water heaters,  electric meters and mailing addresses. 

3. Resale: is there a significant difference in resale values for a duplex compared to a home with an ADU?

4. Rent: I wouldn't think a renter would care if he/ she was renting an ADU compared to a unit in a duplex. Is there a difference in what I can charge for rent for a duplex vs. an ADU?

5. Cost: After speaking with the City Building Department, I learned that there is a minimum deposit for reviews and inspections of $5,000 when I submit my initial development plan to the city, which has a 4-9 month turnaround time. Permitting an ADU takes no more than 60 days, thanks to the new legislation passed in Jan 2020. Is the time, red tape, and extra cost worth converting to a duplex instead of getting a permitted ADU?

6. Permitting: if I go the ADU route, do I really need all associated permits? Eventually, I am going to be renting both units in the house, so I am assuming I want to play it safe and get the potential ADU permitted the right way. But, I have been to many open houses with unpermitted additions in California, so I am not sure.