You need a "transit log" for turkey (Usual thing just lists all your crew and skipper) 150TL The only problem is that you are 'supposed' to clear out each time you go to Greece and then buy a new transit log when you return. (NB. I did say supposed)
If you are starting in Greece then you will have a sailing permit
, for Greek waters, and the same routine applies. (remember I said 'supposed')
There is no 'nationalistic' problem between the two countries just remember to have the right courtesy flag up!
We often have the odd night of two on the Greek islands
just avoid harbours where the authorities hang out!