Any assets you purchased prior to that date are added to the building and depreciated as one asset.
That's not entirely accurate. As you know, residential rental real estate is depreciated over 27.5 years. Not all assets used in a rental property are classified as rental real estate. The furniture you purchased "outside" of your acquisition of the rental property is definitely not added to the cost basis of the rental property, any way you look at it.
Furniture is depreciated over 5 years, unlike the rental property itself which gets depreciated over 27.5 years. So you enter the furniture as a physically separate asset.
However, I "strongly" advise against claiming and depreciating furniture in a rental. It will in time become a real PITA to track. It wears out, gets broken, damaged, etc. and to say dealing with it as an asset is a PITA, is putting it politely.
If you group furniture together and later somethings happens to any one piece of furniture in that group, *YOU* have to go through the rigamarole of "un" grouping things so you can correctly show the disposition of that one peice in the group. Good luck with divvying up the depreciation correctly.
Likewise, if you list each individual piece of furniture separately in the assets section, you'll have a multi-page list of assets that will "never" go away, but will continue to grow as furniture is replaced over time. All you're doing is stretching out and delaying the never-ending nightmare that you will create.
On top of that, many states and just as many towns/cities/counties within a state impose a "tangible property tax" each and every year that an equipment asset is used to produce income. Since furniture is not "a physical part of" the rental property, it's classified by the local property tax appraiser as "equipment" since it is in fact used in the generation of income. So the money you "think" you save by depreciating furniture, you just end up paying to the taxing authority that assessed the tangible property tax.
I would recommend you just expense the furniture under the de-Minimus Safe Harbor act and be done with it.
Under the act, anything purchased for less than $2,500 that meets certain other requirements (and furniture does meet those requirements) can be expensed in the year of purchase, *PROVIDED* they were purchased in the same tax year they were placed in service and were not used for "anything else" prior to being placed in service.
Now while it's possible, I seriously doubt you went out and purchased a whole house worth of furniture in one fell swoop, which "could" give you an invoice exceeding $2,500. More than likely all of your purchases of this furniture resulted in multiple bills/receipts/invoices, and not a one of them exceeds $2,500.
