Would I be making a mistake trading a g35 in for a tt?

The G35 is a rear-wheel drive, the TT is front-wheel or all wheel drive. The TT is smaller, lighter and more refined inside. The G35 is bigger and heavier - it's hard to say which is better, they are two different-cl cars. The TT will be expensive to keep, that's for sure, unless it's a new one. But if you can afford it and you like how the TT drives, sure, trade it, changes are always good.