Regarding hotels: We stayed at L'Etoile in Recoleta. Very nice, nice area and not expensive. http://www.etoile.com.ar/

Next to the hotels are many restaurants ... Rest. Lola was very good.
I also went to a stylish restaurant in Old Palermo (which Gaucho1000K recommended), very interesting, good food..
Porto Madero is also good for restaurants ...