As above, you do need to be very cautious at this entry point.
The GTs body is well protected for rust, but the subframes are not. This is causing cars to fail MOTs due to structural weakness at less than 10 years old. It can be treated if caught early enough, but if not you are looking at c£3k to fix.
Variators will be a potential issue at this age/type of engine, again c£2.5k... yes you can delay it, but at this age its a worry you don't need.
Due to the size and weight the car the front suspension takes a lot of stress, bushes and arms will probably need attention at anything from £500-1000 to put right.
Wheel bearings and the ABS sensor is a common fault at c£500 per wheel.
Cam gaskets, c£400 for the pair.
Of course you may be fortunate and find one with non of these issues, but treat all cars like they have, until you have evidence they do not, and budget accordingly.
£2k pa maintenance and repair war chest for anything else and you should be sorted.
They look stunning, and the early ones can be picked up for high teens... but please don't get bitten and turn into the guy in the pub who slates the brand due to buying a basket case... Best of luck.