Everything worked out fine and we were warmly welcomed by Marinella who showed us around in the apartment. Sadly we didn't have the chance to meet Ernesto himself since he was traveling during the time of our stay. The neighborhood was very calm and quiet and the apartment is located in a nice old building with high ceilings. The rooms were clean and exactly like on the pictures.
The only small drawback was that the second bathroom was being renovated and hence it was a bit difficult in the mornings or evenings to take a shower or enter the bathroom, however, it wasn't that big of a deal.
Anytime again, I'd recommend this place to stay while you're in this beautiful city