We really enjoyed staying in Ca San Marcos. The location is very close to San Marco Square, as well as the San Marco Giardinelli boat stop that you would take from the Venice airport (this is important if you have luggage as it can be very cumbersome if you have to walk a much longer distance). There are many restaurants and cafes nearby, so you will love the location. Even though you are in a popular area, the unit is actually a few narrow streets away from the vast number of people that go through the area, so you will find it generally quiet near the apartment and very few people there.
Inside the apartment, the unit has a master suite that comfortably sleeps 2, and a second bedroom with two single beds placed back to back. This room is cozy for 2 people, but worked well for our 2 daughters. Both rooms have TVs in them. The main area has a table and couches to relax in the morning or during breaks in your day. The kitchen is fine - very basic. I would not expect to do much here except make coffee or handle simple food prep. There were not many amenities available upon arrival (soap, shampoo, coffee, etc), so be prepared to buy/bring that on your own. Plenty of towels provided. There is a washer in the unit and a drying rack, but no dryer. Wifi worked just fine. All in all, the unit is terrific - quite spacious, beds were comfortable and the unit is quiet.
Side note: it was quite helpful to communicate by text & voice with Loredana, and we did so by WhatsApp. I would definitely download WhatsApp and establish connection in advance to help when you arrive.
We loved our stay and look forward to coming back! Venice is amazing!