This provision, through the Affordable Homes Act, make ADUs legal BY RIGHT in any single family zoned property in the state.

Quote from @John Underwood: LOLI'm certain they will add restrictions to prevent people from doing this.

The seller has the two lots legally separated, but due to deed restriction imposed by the subdivision development, found that building a house on the “tennis court” lot was not allowable. 

A 2 +1 is a legal 2-family with a boarder unit that can be lived in by the owner, usually without a stove and you want to make sure the bathroom is permitted.I hope that helps.

CA is brutal when it comes to taxes.I don't give tax or legal advice, but many people believe that holding the property in your name and having a good umbrella policy is a good solution.

What are the pros and cons of each, and which offers the least restrictions, flexibility and cost savings for my intended purposes?

There are no municipal-level rental restrictions. 

To list a few...Anyone who wants to increase their property’s income potential (and equity) and build new housing in a market that struggles with high prices, low supply, and few new construction.House hackers who live in their primary and want to airbnb an ADU love this strategy or vice versaInvestors who want to do both long term and short term benefit from having two separate units.Rental Restrictions on ADUs.Thankfully, Raleigh is very STR friendly and ADU friendly right now.

@Jeet Sangha You need to sign a Deed Restriction for Owner-Occupancy.

Lots of cities have restrictions..Arlington limits to a fairly small area of town, Ft.