1) No. Furniture is not "a physical part of" the structure. Furniture is depreciated over 5 years.
Generally, I do not recommend including such items with rental property. That's because states or lower leve taxing authorities may impose a "tangible property tax" on the furniture assets for each and every year those assets are used in the business . But in your case you have to, since you provided a furnished rental. Your furniture is entered in the assets/depreciation section and gets depreciated over 5 years. If you haven't done that, then personally I would leave it alone and just report the sale of the property "as is" and press on with life.
If you want to include the furniture and you haven't been depreciating it at a business asset as required, then you need to file IRS Form 3115 with your 2020 tax return to "correct" your mistake if the furniture was placed "in service" prior to 2019. Then you "may" have to also deal with state taxes, as well as tangible property taxes you haven't paid on those assets in prior years. That's separate from the 3115. While the 3115 is included with the TTX program, there is no help or guidance provided. The 3115 is not simple by any stretch of the imagination and requires professional help.
Your cost of professional help combined with the penalties and potential back taxes you'll pay for not having depreciated and reported the furniture as required, is most likely not going to help your gain on the sale. So I'd just leave it alone.
