He (most orangies are male) looks way to healthy and well cared for to be just a stray. I'd thoroughly check to see if he belongs to someone before you get too attached to him and start calling him your own. Maybe he was just tempted by the chipmunks in your yard! If he doesn't belong to anyone and your Mom decides to let him in, he should do okay with a scratching post. If he'll be "indoors only" and won't be going out at all, then maybe the Soft Paws claw caps would work. I've never had any experience with them, but some people think they're the best thing to come along since sliced bread!! And when I had my cockatiel I also had 3 Siamese cats, and they never bothered the bird. In fact, the bird would sit on the back of one of them with no problem!
Good luck and keep us posted.