There's no question the cat is healthier indoors. This little guy (or girl) should keep his claws and be kept inside. Trust me, as the guardian of more than a few stray cats, they get used to being inside. Living outside was all this little guy knew, so your house is an unfamiliar concept to him.
Try to make him more comfortable and inclined to explore inside. Hide little treats around the place and put toys in frequented areas. Make sure you carve out some loving time with him. Once he equates safety, food, love and play with his new home, things will be fine.
Your cat will probably always love sitting on the porch, but you'll see the tendency to go outside diminish with time. If he's like one of mine, he'll demand walks after a while no matter what. Yes, I honestly put a harness and leash on a cat and he walks us every weekend. But he loves it and it keeps him (mostly) from going on his own adventures after escaping.
You did a good thing. A great thing. Your new companion will always know this and outside won't be a problem after a little while. I'd love all the cats to roam around too, but it's a much higher quality of life and safety you're offering this little thing. Let us know what you name him/her. Good luck.