Hey,
I have a 17' that I picked up mid December and have since done most of the standard bolt ons, dont have a downpipe yet since its been on backorder since december. I've been messing with all types of cars for quite some time so I'm no stranger to mods either. I'll try and share my insights as best I can and what order I would go in if I were doing it again.
I just did the accessport with a mountune tune and it has made the most significant difference powerwise, although you'll end up with some traction problems at stage 2/3. I probably should have done the access port first, since it already comes with the cobb tunes and you can update the tune as you change hard parts.
I've got the mountune exhaust, not much of a difference in power, but it seemed to help the throttle response slightly. Same goes for the airbox/filter/intake piping, I have an st200 box with ramair filter & piping. Didn't install a big mouth as I didn't want to block airflow to the radiator. I opted to cut the hole in the plastic air inlet above/behind the grille.
Symposer delete was nice to make the car feel less "ricey", best I can describe the stock symposer is it sounds similar to one of those crappy aluminum tube intakes that people put on NA 4 cylinders, albeit significantly quieter.
Honestly, for me, some of the most noticeable changes were the fswerks short throw linkage and a no-pistons gas pedal spacer. Doesn't make the car any faster, but they made improvements in the feel from the driver's seat, if that makes any sense. The less that I need to concentrate on "operating" the controls on the car makes it easier to actually "drive" the car. I would say its akin to adjusting the controls to fit you on a motorcycle, if you have riding experience, then you should know what I mean by that. I'd say the motor mount falls into part of this category as well. The stock one is pretty floppy when you drive the car hard. Mine is a mountune.
I have some other mods too, so feel free to ask if you would like my insights on those. Didn't want to write a novel here.