Woo something I'm good at.
The first gen MS3 does have a few problems with rust. I see clean ones all the time around us though so I think it's just a matter of actually washing the damn thing in the winter. Second gen cars don't have that problem.
The rear motor mount on the car tends to be a bit soft stock. So much so that the engine has a tendency to smash into the firewall as it starts to wear out. It's pretty common to replace it with a unit from one of a couple of different manufacturers.
Turbos are an unknown quantity in the cars. First gen cars have a tendency to smoke a and bit there's a TSB to change to 5W-40 to prevent that. Otherwise they last anywhere from 25k miles to 200k miles. I broke the journal shaft in mine at a bit over 24k.
A quick way to start an argument is to mention oil. Supposedly Mobil1 doesn't tolerate gas in the oil very well as it's a class III synthetic. It's pretty common to run Rotella T6 5W-40, as it is a class IV, in the cars. It subjectively quiets them down a bit too.
Second gen cars have an issue with the dash that has caused their warranty to be extended. If the interior of the car gets really hot it separates right above the info displays on the dashboard. There's also a recall currently on second gen hatch gas struts and the seatback adjustment device.
Both generation cars have an issue with fueling above 5500 RPM with the stock CDFP internals. CS or Autotech internals take care of that issue.
Any direct injection car suffers from "Super Knock" if you flat foot the throttle at low RPM in 5th or 6th gear. When you're driving one you want to be at 3000 RPM or higher before applying large amounts of boost. Otherwise they have a tendency to install a viewing window in the block.
Since you're buying a used one make sure that the Accessport is unmarried from the car if it was modified. You won't be able to change the MAP or reset the ECU back to stock if it was not. Also make sure that all the mods with the exception of the CDFP were removed. The car does not tolerate larger downpipes or intakes very well on the stock map.
Other than that the car has an issue with carbon buildup on the back of the valves so a catch can with a check valve is highly recommended.
It's pretty simple to make stupid amounts of power out of them with some basic parts. The stock engine is supposedly good to about 400 HP and FT-LBS of torque before it becomes a bomb.
I'm about 45 minutes north of you in the Poconos and I work in Easton. If you want to drive my modified example prior to making the decision you're welcome to it.