There are coastal commission guidelines in addition to the zoning and building department requirements.

If I were you, I would look into the HELOC to access your additional equity.

Additionally, the schools for this neighborhood are excellent.

I do however, think that it would present a very unique opportunity for a buyer with children whom wants to relocate from the city (easy commute in) and perhaps have additional rental income, OR move the in-laws into the ADU. 

In addition, try to network with a realtor who may have some buyers that had deals fall apart.

In addition to the educational components you mentioned, I suggest you network with like-minded investors locally to you and in the areas where you plan to invest. 

Does UMMC offer any incentives in addition to Live Near Your Work?

I could easily put in an additional 30k or so and purchase something in the range of $800K.

A full review is required when a primary buyer is putting less than 10% down or when an investor is putting less than 25% down This review requires a long form questionnaire, budget, by-laws and possible a couple additional documents. 

Therefore, you can deduct items that are directly related(repairs) to the rental units plus items paid indirectly for the rental units(think real estate taxes, interest, insurance).in addition - it looks like you are looking to use parts of the personal residence as a home office.Just note that, it would be hard to prove that you use 100% of the personal residence as a home office.