Yes. It's easier to consider the ADU like separate structure and depreciate it over 27.5 years. Any work you do to get the property ready for renting is classed by IRD as capital improvement including architect design fees, and is not fully deductible. Depreciate the total cost of the improvement from the date placed in service (ready to rent).
Furniture and appliances used in rental property will be 5 years depreciation. Hopefully, you have a separate meter for electricity and utilities. Otherwise, you can use any reasonable means of allocating those expenses.
Please feel free to post any additional details or questions in the comment section.
