Your ordinance, read for your lot
Size caps, height, setbacks, owner-occupancy and parking, answered in writing before design starts.
Rental is a separate question
Whether you may let it, short or long term, is decided by the ordinance and sometimes by an HOA. It can change the design.
One permit path of its own
An ADU is a dwelling. It is permitted and inspected as one, not as an outbuilding.