New landlord (ADU in backyard); are we now a business?

Hi,

I am a first time landlord for tax year 2019.  One of the issues I still have questions about is whether I am now a business, and can therefore utilize the Section 179 and/or TCJA “pass through” depreciation calculations.  I have read conflicting things.  Some made it sound like even renting a room part-time means you’re now a business, or that it’s almost self-defined.  Others made mention of being certain you are working at least 20 hours per month year-round on the property.  (I probably was at first during construction and while getting it ready; not sure if that’s true now, perhaps if gardening is counted?). Can I self-identify as a business, for tax purposes?  I have not purchased a business license as of yet, perhaps that’s my answer?  Thank you for any help or guidance!