I spent a little over 2 weeks in Turkey back in 2007 as a solo traveler and loved it. Your itinerary looks very good - somewhat similar to mine. I wound up staying 4 nights in Istanbul at the beginning (then 2 at the end), then 3 nights in Cappadocia, 3 nights in Fethiye and 2 nights in Selcuk (Ephesus) with a day trip to Izmir on the way back to Istanbul and then, like I said, 2 more nights in Istanbul before I left. I mostly traveled by bus, which I really enjoyed but maybe not to everyone's liking. Their bus system is wonderful, though - luxurious buses with movies, reclining seats and so on. And it's a great way to meet people.
I did not do any tours, although at the place I stayed in Goreme, the owner told me that his assistant would drive me around for the day and show me lots of things I couldn't get to by bus or walking. That was an incredible experience and all for around $20 (plus tip). I saw a lot of the caves and many other sites. Alton even took me to his house and I met his mother and sisters and had tea with them. That alone was worth it. Sadly, the hotel I stayed at is no longer in operation. Alton and I still keep in touch on Facebook. :)
In Fethiye, I went on a boat cruise for the day, which was wonderful. We made several stops and went swimming, then had a wonderful lunch on board. I was the only American - it was mostly other Europeans with me.
If you are interested, I wrote an online journal of my trip when I was there with some photos. Obviously it was a while ago but it might be helpful to get a feel for the place. https://mardeeinturkey.wordpress.com Turkey was absolutely wonderful - probably one of my most favorite destinations. The food is incredible, and the people are the friendliest and most helpful I've ever met. One man actually walked me 4 blocks to the bus stop when I got lost, which was completely out of his way. :) If you get a chance, learn a bit of Turkish before you go. The locals will really appreciate it.