I had a great stay in Istanbul and Aslinaz couldn't have been a better host. She answered her messages immediately if I had any questions or problems (which I didn't).
The flat is right in the center of the action, with tons of restaurants, shopping, nightclubs, bars, antique stores, and coffee shops. Even though many tourists visit this area to play in the evening, it doesn't have the touristy feel of Sultanhamet, which of course you'll also want to visit for all the historical sites, the grand bizarre, etc. The flat can be pretty noisy into the wee hours of the morning on Friday and Saturday (the area gets very very crowded), but part of being on vacation is being out with the locals dancing, drinking or hanging out so it shouldn't bother you. But pack earplugs if you plan to go to bed early. I particularly enjoyed exploring all the antique and unique hipster shops in the area as it had a "soho of Istanbul" feel to me. Really enjoyed my stay and Aslinaz is a wonderful host.