Good place right in the center near Galata tower. The heating is thru a gas heater installed in the kitchen so you can make it as warm as you like. Although there are technically six sleeping places, i would not think more than four would feel comfortable as the place is not too terribly large (three separate rooms and a larger common space adjucent to the corridor). There were three of us, and it worked well. The toilet/ shower are small, but not inconvenient and clean.
Omer was very efficient in meeting us on the street and showing us around. The terrace is on the top of six floors where you walk up the stairs from the appartment located on the ground floor. The views are stunning and hard to come by - from a high point you will see the Golden Horn and Bosphoros with all bridges, ships, sea and architechture on the other side.
If you come with luggage that you can carry up about 50 steps, ask you taxi driver to take you to the lower street (Bankalar Cadessi) and drop you near Vakif bank on the corner and just walk up the stairs - it will save you a lot of time in the cab wiggling on the narrow steets and (like with us) not knowing where to go next.
The place is over a 100 years old and full of local flavor, i would highly recommend it and would gladly come back.