08's have a banjo bolt filter screen. All turbo Subies do. Some have more than others. It is a myth that 008+ do not have them.
During the 2008 Stop Sale some overzealous Subie techs removed them pre-purchase. this was not advised by SOA. They were there when the cars left the factory.
Boost level is somewhat determined by knock/timing/fuel/etc. If using a stock turbo, a PW is major overkill. But, if it makes you feel better, its your money. You will most likely be able to (safely) tune to 18.5-19psi on stock fuel, stock turbo, PW. Might be able to eek 20psi for a quick second.