Technically the code says 70 square feet for one person minimum of dimension in any direction 7 feet.  

If that is your dimensions you are good then. 

@Robert Palladino I talked to my contractor last night and he said that a 14’ wide lot should net 13’ wide brick to brick inside dimensions just like the house he’s renovating now. 

JT,(A) One accessory dwelling unit and one junior accessory dwelling unit per lot with a proposed or existing single-family dwelling if all of the following apply:(i) The accessory dwelling unit or junior accessory dwelling unit is within the proposed space of a single-family dwelling or existing space of a single-family dwelling or accessory structure and may include an expansion of not more than 150 square feet beyond the same physical dimensions as the existing accessory structure.

1) It is not yet clear but it seems that you will be grandfathered in at the time when the changes occur in regards to occupancy changes.2) Per AB-68:"(A) One accessory dwelling unit and one junior accessory dwelling unit per lot with a proposed or existing single-family dwelling if all of the following apply:(i) The accessory dwelling unit or junior accessory dwelling unit is within the proposed space of a single-family dwelling or existing space of a single-family dwelling or accessory structure and may include an expansion of not more than 150 square feet beyond the same physical dimensions as the existing accessory structure.

I'm just using the basic parcel dimensions from various muni GIS files and Microsoft's awesome building footprint file https://github.com/Microsoft/U... for the building footprints on the parcels.

So you end up paying a premium for corrugated metal sheeting as your exterior material but with the catch that you have confined yourself to set dimensions of the container. 

Do the lot dimensions and frontage support a dedicated driveway or will it be shared?

All of which are normal dimensions for minimum bedroom space.

Dimension 26'X53' which is pretty close with 1254 sqft.