We had no problems finding the apartment as Alessandro met us at the water bus stop (after easy communication with him by text). The area was even better than we expected - real Venetians still live there making Via Garibaldi a varied main street only minutes away from the B&b. However, you can walk to S.Marco Square in 15/20 minutes!
We would stay in Castello area again.
The apartment is brand new and Alessandro is a highly cooperative host.