Staying at Yakup's apartment was a very good experience.
The place is located at a 6-7 minute walk to the Cemberlitas station which is pretty much the center of the Sultanahmet area. The walk from the apartment to the station is quite uphill but still manageable. There are many shops, restaurants and hotels in the apartment's vicinity so buying groceries or finding a place to dine out is really convenient.
The apartment itself is spacious, well organized and has all the facilities. It is on the 3rd floor and there is no lift, so people with heavy luggage could face some challenge, but other than that, it is a good place to stay at.
Yakup is an absolutely wonderful host, he is always available, responds immediately to your communications and is VERY helpful.
We would definitely recommend this place to our friends visiting Istanbul for a short or long stay.