This is an excellent (very) large apartment, very well located in Sestiere San Marco, about a 5 minute walk from the Piazza San Marco (via Campo San Moise), 5 minutes from Academia (via Campo San Maurizio and Campo San Stefano), and less than 10 minutes from Rialto (via Campo San Anzolo, Campo Manin, then Campo San Luca). It less than 3 minutes from La Fenice, and less than 3 minutes from the vaporetto station Santa Maria del Giglio.
There is an excellent supermarket (Simply Punto) less than 5 minutes away via Campo San Anzolo, and if you know the way, you can reach it most efficiently via back streets that avoid the touristy ones. I highly recommend investing in a copy of "Campi, Campielli e Canali" (the most recent edition costs about 29 Euros, but an older edition which can be just as good costs less) as the one and only serious book-map to know your way around Venice.
It is not as high as one thinks by counting the number of stairs because the building is such that the stairs are lower than usual (let's say in Paris), and my family and I had no problem at all climbing the stairs up and down a number of times a day.
I did not meet Andrea who was on a long boat trip, but his friend Manuela who manages the apartment was a model of kind hospitality and professional efficiency.
I had a wonderful time in Andrea's very well located apartment, was not happy at all to leave, and I highly recommend it, particularly for long-term family stays.