Actually only part of the 9W 777s are going to Turkish, not the full fleet. 3 or 4 out of 7 of the B777.
A330 is the best option for GF, obviously.
That depends. Economically speaking, 215 seats is not enough to make things work. You need a higher density arrangement (I estimate an A330 needs to have at least 240 seats to economically justifiable, but this could change with cheaper fuel prices).