Just ordered our entrance gate yesterday.

We did everything in our power to deal with the issues that came up (including trying to seal possible entrance points of the smoke).

We're running similar numbers at our family residence, a 3300 sq ft Victorian in a beautiful, small, gold rush, tourist town in CA....walking distance to the historic downtown which enables us to rent out a tiny studio apartment on the first floor via Airbnb for 3-4 times the rate of a long term renter.Also, converted one of the master bedrooms with a private exterior entrance into another small studio by simply closing off an interior door, renting that out, too.Leaving our family with a high end, private 2500 sq ft house with 4 beds/2 ba, family room, dining, living, garage, etc.

I have one key for every main entrance and each unit. 1 key is way better than 10+Mechanical screw to the side of the house lock boxes. 1 per unit and 1 for myself and people I send to do mx and repairsFor the unit lock box I give just that unit the code and explain to them that if they come home hammered and can’t find their keys I’m not coming to let them in.

Each 350-500sqft unit could be self sufficient with its own entrance, bathroom and small kitchenette but still have access to a shared common kitchen.

If they don't have their own entrances to outside, that may avoid the zoning requirement by making them more of a "mother in law suite".

We also have a guy living in the basement and he has his own entrance, kitchen, bath etc... and it's fantastic. 

If the lot is big enough, then a well-designed ADU (with their own private yard and entrance) should NOT interfere with the life of people living in the main house NOR should it decrease the quality of life of the people living in the main house.

It’s a nice additional feature and it’s right at the private beach entrance.  

I could still have a separate entrance for a potential Tennant but that connecting door is key (no pun).