I have a 2004 Outback with the EZ30 3.0R engine in it. Being an Outback, it is an auto.
The engine is lovely, quite amazing actually, doesn't seem to run out of pull and has very good pull over the 3500rpm mark, when it really comes to life.
The things people say to watch out for is the engine burns through quite a bit of oil, so that is something to watch out for, and head gasket issues. Obviously the lower KMs the better,
Best thing to do is get a tune, which will help with the fuel consumption and open the engine up a little more as well, which is nice. A little more low down torque.
Best gearbox with it, from what I've heard would be the 6spd manual box, which would be a pleasure to drive, but the 5spd auto is "buttery smooth" as well
Other than the burning through some oil, and headgasket issue at high kms, I don't think there is much else, but search around the net. Google is your friend.
All the best