Whether you are investing for Cash flow, appreciation, looking for value add, or just tax benefits.I first build out my buy box, which the more narrow it is, the better (multi family, 3 units, in XYZ zip code, at this price point per sqft, build after XYZ year......). 

I have recently become incredibly interested in real estate and have been studying up in all my free time for the past month or so.

Financially analyze your investment, including expected rental income versus expenses such as taxes, insurance, and vacancies.

You may pay $10,000 in interest but you only get back $2,000 back in tax savings. $2,000 is just a random number, the exact number depends on your overall tax situation.Building an ADU if you plan to rent it is business interest, not personal interest.

This property is mortgage free so no issues there.

Any multiple state tax implications? 

I can't tell yet if it is free standing or not, will find out today, but either way could be an issue. 

will this help anyone who uses property managers and keeps QB for taxes, mortgage, amortization and depreciation?

Ensuring clear contractual terms and maintaining good communication will help protect your interests.If you have any further questions or need more specific advice, feel free to ask!

Downside is when it comes time to sell, I would be hit with depreciation recapture tax.