Ditto with what John said, with perhaps a few side notes.

Not all unfurnished apartments will have no light fixtures, this depends on the owner. Also, remember you can negotiate with the owner to jointly select basic fixtures and have him/her (ie. the owner) purchase them, then place them on the inventory which will be checked when you return the property. As for the air-conditioning, central air conditioning systems in residential property are not common here in Argentina. Split-system aircons are the norm. This allows you to buy the units you think you need for each area of the house you think its needed. Similar to the light fixtures... I would suggest speaking with the owner and working out a deal whereby you would "invest" a couple of months rent in aircon units and those would become part of the apartment furnishings, etc. etc.

In the end, it all depends on how much time and work/effort you are willing to put into making the deal.