While Istanbul is a brilliant City to visit, it's not a place that will tolerate hundreds or even thousands of boozed up fans singing, partying ect
There is a bit of a cultrul difference regarding alcohol & drunken behaviour in many parts of Turkey including Istanbul
(Not that I would expect any bad behaviour from City fans)
The ground is a bit of a distance from the City and is pretty isolated
Don't get mixed up with the airports as there are two main ones, one in European side & one in the Asian side
An evening cruise on the Bophrus is well recommended
If any one does go might be favourite flying to one of the resorts like Bodrum or Izmir & just fly to Istanbul for the game as flying time is only an hour & flights only about £20-£30 return
If you do go give the locals plenty of respect and they will welcome you with open arms