Eren is a great host, the communication was super easy. The apartment is conveniently located very close to the Istiklal Cd. (5-7 min walk, but mind that it's central Istanbul, so you'll get some steep hills), 10-12 min from Taksim and you can also go downhill to the Modern Tramway. If you make do your research beforehand, you can always choose a route that it's convenient, so you don't need to warry about "climbing" too much.
Regarding the apartment, very spacious, probably one of the largest ones in the area, everything was clean and pretty new. Did not eat inside (doh, it's Istanbul), but it seemed that the kitchen had most of the things you need. Another plus is having an elevator.
I would recommend this location because it's on a quiet street (so you don't hear a lot of honks and yelling), but you're still very close to whatever you need - coffee shops, restaurants, transport etc.