I'm not so good at horse buying advice but I'll try. I see a bump on his head, and his feet look odd. He sure is beautiful though! I would get a vet to check him over before you buy him though. The head might not affect him, theres a horse at my riding barn with a bump on her head and it doesnt seem to bother her too much. I'm not sure about the artheritis if your going to to be doing only light riding it might no be too bad.
Ask a mare, tell a gelding, and discuss it with a stallion.