If you have one invoice from the designer (who purchased all of the furnishings), there is really no reason you could not use that total (i.e., "lump them together") and depreciate the total over a five-year period (furnishings for residential real estate rentals have a recovery period of five years).
The foregoing method could have negative implications should you decide to dispose of or otherwise sell one or more of the items (less than all of them) as you would need to make an allocation for the item(s).
