Depends. I personally would do the intake. Try to get as much air as possible to the throttle body by eliminating turns and narrow passages in the air intake. More air/presure equals more power. The engine will be able to breathe but you will lose a bit of power if it can't breathe out. If you want to do the exhaust make sure the exhaust pipes are up to spec. The entire system (inlcuding the catalytic converter if possible) makes a HUGE difference if you replace more than a muffler. As far sites, subarupartsdepartment.com is good for OEM. Performance sites usually are specific for model years...look around for your model year and then go from there as far as performance...
