Maybe you can put up a wall and add a door and now you have a 5 bedroom.

I could also wall off half of it to decrease that commercial footprint.  

I personally paid for similar ads in the local Houston newspapers, and regional edition of the Wall Street Journal.3.

I see on LA County guidelines and CA HCD guidelines that, when converting a detached accessory structure into an ADU, the structure can be expanded by up to 150 sq ft in order to accommodate ingress/egress.Does anyone have experience with using the 150 sq feet rule?

Quote from @Jaron Walling: You should already have insurance on this property BEFORE closing.  

Opening a few walls, updating kitchens and baths, flooring lighting, etc.

Opening a few walls, updating kitchens and baths, flooring lighting, etc.

I think if you were sharing walls or in same house, then certain quiet hours in lease or noise restrictions can help prevent some issues. 

There may be ways to share space but give the impression of a separate unit (such as an unpermitted wall up to create separation). 

In my area, not only is there zoning regulations, but building regulations where 3 families are built to different building standards, such as cement walls for boiler rooms, sprinklers, fire escapes to name a few.