That's a lot for 10 days.
- 3 full days in Istanbul is good. You could do more, but 3 is good.
- I wouldn't go out of my way to go to Gallipoli. It's a good break on an otherwise boring drive from Istanbul to Troy, but it wouldn't make the cut for me on a 10 day trip.
- Day 6: Are you thinking about going from Izmir to Pamukkale to Fethiye in a single day???? That's way too much if you want to see anything at all at Pamukkale. You have at least 3 hours from Izmir to Denizli, then transfer to a minibus to Pamukkale, then time at Pamukkale, then back on a minibus (or taxi) to Denizli for another transfer, then another 2.5 hours from Denizli to Fethiye. I wouldn't do it, although admittedly I do tend to travel in the slow lane.
If you are interested in Troy, you need a good (human) guide to help make sense of it. Otherwise, it just looks like a pile of rubble. (I understand that they have opened an interpretive museum since I was there in 2015, but still ...)
I am glad I visited Pamukkale, but it wasn't my favorite place in Turkey. It's very over-touristed.
I learned to love Antalya during my time there. It's a great base for exploring a bunch of ancient sites, and the transit options good. Sites worth visiting around Antalya include Perge, Termessos, Phaselis, Olympos, and more. (Hint: there aren't any beaches, or at least what I would consider real beaches, in Antalya.) Sagalassos is my favorite spot in the Antalya area, but you pretty much have to rent a car to get there.
I would keep the Istanbul plans, consolidate around one city (Izmir/Ephesus/Pergamon, Fethiye/Saklikent or Antalya), and keep your Cappadocia plans. You might want to consider flying from Istanbul to one of the other cities and then take a night bus to Cappadocia.
