1. The most interesting route from Istanbul to Calis is along the coast road. It takes you out to Canakkale, Izmir, Aydin and then to Fethiye. Alternatively, the 'mountain route' is via Eskisehir, Kutahaya and Isparta.
2. Pretty much the same applies to Antalya to Calis. You can take either the 'mountain route' via the D350 through Korkuteli, or the D400 along the coast via Tekirova, Kas, Kalkan etc.
Obviously, if you decide on the 'mountain routes' you'll need to be aware of the weather forecasts as even in September and March there can be problems with snow.
Whichever routes you take there are plenty of places to stop along the way at sites of interest. You could make some short diversions too to see Gallipoli, Pamukkale, Kas and Meis.
