New Chinchilla Health Questions

So I recently got a new chinchilla named Carlos last week because I wanted my other chinchilla ChiChi to have a friend. I've had chichi for about 8 months now and he turned 1 in May. I was told that Carlos was 2 or 3 when I got him last week. Carlos and ChiChi do not get along so I might be getting rid if Carlos if it doesn't work out because the only reason I got him was for chichi to no be so lonely. But I have some concerns for Carlos. For starters, he bites. If you go to pet him anywhere but the top of his head, he turns and nips you and it hurts sometimes. I use gloves to get him out of his cage. Also, he seems very overweight, when I got him, you couldn't even see his hands when he ran but ever since I got him a wheel and let his have long playtime outside the cage, he looks healthier. Also, he seems kind of cross eyes if that makes sense and he is missing a fur patch under his eye and behind his neck. The people that had him didn't take very good care of him AT ALL and kept him out in a barn with horses and spiders all by himself and when I got him, the woman didn't even know what name he was given by her 11 year old daughter. So in a way I feel like I sorta rescued him from death. And the box he came in from the lady had spiders in it so I let her take it back and I put Carlos in a small cage I brought. And the alignment of his back looks weird and out if place and I feel bad for him because he's still a living animal and he can be a sweet heart. But I don't know what to do about his health or if time will help him heal. Or should I take him to the vet? Thank you all so much for the help😃