Watch out for the class names as well as the UHS speed. Class 10 should be the bare minimum, but you should get a high UHS number (probably a UHS 3 would be nice). If you take out your card, you can see a number in a C. That's the class number. A number in a U is the UHS number.
Otherwise, it's all good. If you're buying a card and money's not a huge issue, just buy a 32 GB card. I think it's the largest that'll fit in it. I'm not sure if SDXC can work... I'd stick with 32 GB. Each full game (downloadable games like Pokemon, Fire Emblem, and Animal Crossing) takes about 1 GB so that's not bad...