Hi, sort of late on a reply here and am not sure if you purchased that (IMHO) high mileaged GT.
For the price I'd like a few less miles on the OD.
But if this falls in your budget and it drives ok (since you said this is your 1st American car, it is a MUSTANG so I like your style!)
Can I assume the cars you drove previously were European styled? If so, the Mustang is not a handling car like some European automobiles. Doesn't mean it can be like them but stock I will say doubtful.
Sorry back to my reply.
Personally I would look at in this high mileaged Mustang
Check for any body issues.
*Rust, bondo, has or was this car every in an accident? if being sold via a dealer, I believe even in the US this must be disclosed.
*Does it require an alignment? does it drive straight?
*Hit the brakes in a safe location , (back of a parking lot for example), does the car pull to one side? If so, brake job may be required.
*Is there any pulsing when the brake pedal is applied? possible indication of worn rotors. Machining them maybe required.
For the motor;
*check for any obvious signs of an oil leak. In the engine compartment, look underneath for any drips.
*have the sales person start it from a cold start, with you standing behind. Watch the dual exhaust, look for any smoke at start up. A small bit ok; if blueish and a couple seconds of time or more, err walk away.
*place your hand in the exhaust stream and get a wiff of the exhaust. If it smells sweet, maybe an indication of radiator fluid being burnt during engine combustion. Not good.
Just a few thoughts, best of luck in your purchase. I love the Ford Mustang - always have -. 45 years and going strong.