I had such a wonderful stay at Hakan's and recommend a stay! It's quiet away from all the hustle, and the window view is lovely with the trees outside. Hakan is thoughtful, kind, and willing to help with recommendations and questions. Internet is fast, and the space is comfortable, and I appreciated having the desk as a dedicated workspace.
Besiktas is an excellent area with lots of restaurants and cafes. The M30 bus line will become your friend to get up the hill to Nisantası, and you can walk down to the ferry terminal to explore other parts of Istanbul. Hope to be back again!