Congrats on the Subie!
Wheels can be pretty expensive, especially good ones. Of course you can get steelies for super cheap, but if you're looking to upgrade, I'm guessing youll spend more than $150 each, easily. I have LP Aventure LP3 and I love them. Method Racing also makes a lot of good wheels.
I had my wheels put on when I got new tires to save on installation cost. If you are looking for good All Terrain tires, I would recommend Falken Wildpeak A/T Trail (but check the sizing for yours). They may be overkill if you dont live in a place with much snow or don't do much driving off pavement. But they are fantastic tires and much lighter than the BF Goodrich KO2's, so they don't impact MPG as bad or suck up as much torque, which the outback is a bit limited on.
There are a huge variety of roof baskets. But I can't think of any general criteria or considerations. Aesthetics is one thing, and maybe aerodynamics. I am not sure what your crossbars are like, but on my 2015, they're pretty wide so make sure the mounting hardware will work. I have Thule Trail XT which I found on Craigslist for much cheaper than new.
You can see how it all looks on mine in this post.