Congrats on your new car and welcome to the forums!
Now before you start posting, please keep the following in mind:
1. Your car is brand new. Yes, it's just a new year, but for all intents and purposes, it might as well be a Jeep Cherokee as pretty much 100% of the car is new.
2. Will XXX fit my car? Probably not. The turbo is different, the intercooler is different, the exhaust is different, etc.
3. When will manufacturers start making XXX parts? We don't know, please bug the manufacturers.
4. I found XXX parts that will fit, can I bolt them up? Your best bet is to wait for engine management before you start bolting up things. Each car has something called open/closed loop fueling issues mandated by the EPA that can negatively affect vehicle modifications. The wise/safe course of action is to wait for engine management then modify. Yes, you can probably safely get away with simple mods, but the smart thing to do is engine management first, then parts.
5. But I found out that XXXX from an older Subaru will fit on my 2008. Well post that crap here and we'll update this for all to see.
If anyone sees anything to add, please post. The genesis behind this post is to prevent 9000 posts of will XXX fit my 2008. This is an annual annoyance and I'm hoping this may stem some of that.
Old parts that WONT fit:
Rear sway bars
Intakes for Legacy GT
Old parts that WILL fit:
Downpipes for Legacy GT
BPV/BOV for Legacy GT
Lightweight crank pulley
short throw shifters/bushings
front sway bar
TMIC for Legacy GT
FMIC for Legacy GT (may have to mod to fit)
Turbos for Legacy GT
Clutch and flywheel
contains a huge list of parts that will fit 08/09 cars
STI Exhausts that will fit