First things first, if you do decide to get him I would just work on getting his weight back on. The pictures don't show him in very good poses to judge on weather he has bad legs yet or not. To me, from these pics, his legs look OK. They're not great, but they're not completely horrible either. He's still growing, so he might look a lot better in another year or so. His neck is what catches my eye. Looks like he might just need a ton more muscle. If you've wormed him a few times already, and his stomach is still that big then... He either has some serious worm trouble or his belly was stretched from it in the first place. This will probably take a while to go down. Don't give up on him! He might just need a little TLC, and he may just be the perfect horse.