First thing is you never want to close on a development parcel until you get all of the approvals and permits to build what you want.That being said the best thing to do is call the city and ask them what the attitude is towards development in that area and what your chances of approval or denial look like. 

We received permits from the city to build a master suite with a full bath & walk in closet.

Reading the gov site, it says, I need zoning permit if I am renting between 90 to 180 days per year.

I'm curious what kind of work have you done on your properties and your experiences working with the different building departments around the state.I was just reading our city code and found a permit exemption for replacing water heaters in 1 & 2 family dwellings as long as the venting and fuel source were identical.

Permit office

Just randomly came across this, might be too late @Ronak Patel but if your title and legal description says you own two lots you might NOT need to subdivide it; it's already done for you.ADU you can get it permitted and built quicker, but I don't think it'll add to the exit value as much since most appraisers and market resale is not treating it at the same dollar per sqft as regular SFH (but it's pretty close in some markets I've seen like in Long Beach).4,000sf lot is still manageable.

Will you take care of Inspections and permits?

You need experience and knowledge in; soil suitability, EPA guidelines, Department of Transportation requirements for highway/road access, road development, zoning and permitting, accurate bidding, utility management, life/safety requirement and so forth.  

Just make sure to do a true apples to apples comparison, and ensure quotes for utilities, foundation, trenching, site prep, permits, finishes, appliances, etc. are included.Renting out the ADU is a great strategy!

City is NOTORIOUS for requiring permits for EVERYTHING.