They're not a rare breed....they're not really a breed at all. He's likely either a Presa Canario labeled as an American Allaunt to rack up the price, or a big molosser mix.
Health problems they're prone to are going to be the same as the Presa or other large breeds...hip and elbow problems, skin problems, and epilepsy. I think mostly except for the joint issues, they're relatively healthy. It's unlikely, but were the parents of the dog health tested and certified?
As far as raising him, you're going to raise him the same way you'd want to raise any other large, protective, molosser type breed. Mainly lots of socialization and lots of early positive reinforcement training, setting good boundaries, etc.