Hi, welcome.
I have a wrx hatchback so not the same but similar.
Induction kits are a pain most people don't bother as you need a map after it's been fitted but the stock air box is very good so only reason to do it is the sound.
As for the bov again if you are going vent to air it needs to be mapped onto the car.
For noise I am not sure how many cats the sti has but removing one along with a resonator will get the sound up for you.