I cannot answer the first two questions, but I can tell you that my dad is growing mamey seedlings successfully in St. Pete. They do look much worse during the colder months, but they grow back and look healthy again once it's warmer. I have seen a grafted tree set fruit in St. Pete also, but I do not know if that fruit reached maturity and the last time I saw the tree it didn't look amazing, nor did it have any fruit on it. Occasionally we'll get frosts in St. Pete, but it is not common. Homestead is really where the mameys are grown commercially, from what I understand.
That being said, I'm sure mamey could fruit and do well in other areas!