The ms3 you say? I may know a thing or two about those-
To answer a question that may previously have been answered- Ms3 is available with cloth seats. You'd be looking for a Sport Package, as opposed to a GT package. Prior to 08.5, the GT package had leather bolsters/seatbacks/headrests, and the same cloth centers as the sport model. After that, the GT package replaced the centers with alcantara. With the sport, you also lose the Bose (no big deal) HID's (easy enough to do, since all cars were equipped with projectors) rain sensing wipers (I like em, but they're picky sometimes) auto on/off headlights, and LED taillights. All cars were equipped with TPMS- and the sensors are in the wheels themselves.... so if you're a wheel whore like me, your TPMS light becomes a regular fixture on the dashboard.
People have previously mentioned the weak PCV, and they're right.... the stock PCV setup in the car SUCKS. Mine's fouled out after about 50k mi. Replacing it is not a real treat either, because from what I've seen, you have to get behind the intake manifold to do it, and that is a real treat in and of itself.
The rear motor mount is also known to fail, though less prevalant after 2007. There was a factory recall to replace the mount, if your potential car has NOT had it done, do so. I had mine fail on a road trip, and thank god I was 10min from a truck and a trailer I could get, because it shredded the entire driveline assembly on the drivers side of the car. (new axle, CV, etc etc).
Rear shocks have been known to be weak, though I've not experienced that personally. Seems that it's more prevalant with the let's slap some lowering springs on it and call it good crowd, though the jury is still out.
Turbos have also been known to eat seals.... AGAIN- it's with the modding crowd. Seems that poor tunes, downpipes w/o said tunes, and shoving it past like 19-20psi is the likely culprit..... same with the rods.
The biggest problem with this car is fuel. Always has been, always will. The injectors are MORE than capable of flowing anything you have to throw at them (seriously, 400+whp 3076 builds and STOCK injectors are at like, 38% duty cycle, it's just silly.) The problem is the CDFP (cam driven fuel pump) on the top of the engine. It's notoriously weak, and has been known to fail under high pressure. A lot of the popped motors/fragged rods/miscellanious horror stories you've heard can all be traced back to weak fuel. Various solutions abound, from uprated internals, to a whole new CDFP built for high HP applications, to one guy I know actually ran twin Walboro electrics up top. He won't tell me how the hell he tuned it though.
Now for the fun stuff-
This car responds VERY well to opening up the intake/exhaust side. An SRI and a mid/test/offroad/don't get caught in CA pipe is worth ~20whp.... been verified on multiple occasions, on various dynos.
If you wanna get tricksy, look into an aftermarket intake mani. I won't name names because I am sort of (my website anyway) sponsored by said people, and I didn't exactly pay for it, but I have a stage 3 ported intake mani that saw me gain 100cfm airflow. The ports themselves were varied like 25% from 1-4, and the VCTS was nothing but a way for air to not get where it needs to be. I'd be happy to point out where said part may be purchased from, and there are flow benches and dyno sheets on it as well, but I don't really wanna violate any rules regarding advertisers and whatnot, so I'll wait for clearance from Big Brother. Anyhow, the short of it was, I gained 100cfm flow, spooled approx 400rpm sooner, made ~+5whp ( could have been other tweaks I made at the same time, so tough to say... but it made more power than the car right next to it, with my identical mods, on the same dyno, back to back) and LOST 3 PSI. Should be LOADS of fun once I get 'er cranked back up.
Tuning is fairly easy, and there are a couple of crowds on this one. CP-E and Cobb. Cobb has recently released v2 of the AP, and people are seeing some pretty hefty numbers with the AP and AccessTuner Race. CP-E standback has been the go to for the big number guys since it came out, because of some internal flaws in Cobb's initial design that sent out wonky boost spikes and whatnot. I don't know about Cobb- but I know for sure that CP-E's tuner is capable of tuning for E-85, and that's worth some good power. IIRC, a STOCK cx-7 (same motor, smaller turbo) gained close to 30whp on an e-85 tune, no other mods. Now I don't know if the boost was cranked up on that one, so don't hold me to it.
Overall, the car is a lot of fun. I see ~28mpg mixed driving on a fairly regular basis. Clutch is strong, handles fairly well, and is practical when it needs to be. I'm sure there's more to the car I'm forgetting, so if you have any questions, don't hesitate to ask.