Personally, I would consider skipping Europe and shipping directly to Istanbul from the US.
Riding through Europe will be VERY expensive and may cause you to make compromises/sacrifices during the latter sections of your trip.
Furthermore, for future travel purposes, Europe is and easy/cheap destination to arrive to...whereas the other bits of your itenary are not...even discounting the political instability factor.
Spend your time and $$s in countries that could use the tourist income...consider it a charitable donation of sorts
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