Quote from @Matt McNabb: I'm a solid $400k/yr job in NYC and have $250k to begin investing as my first step into building a portfolio, although I don't have time to be a landlord so I have to account for management fees.  

This Wikipedia page gives different wall types and how well they block sound.  

So when you build your pocket neighborhood, which is an interesting concept, what's to stop an undesirable person from moving in.

Building an ADU is not like building a structure on a vacant lot.

Do you know how I should go about to find  a trustworthy and fair GC for ADU build in North Hollywood? 

No matter where you settle upon, your idea to build really comes down to your goals.

Speed of building a portfolio (Cash-on-Cash return is a factor here)?

I also really like the idea of building a brand that you could sell.

At least most cell carriers will auto-block them. 

Wish they would build houses with this style of architecture still.