I love chameleons!
We've worked with panthers and melleri. Our current panther is not aggressive at all.
If your thinking male, I would go with the xlarge cage. Males will roam more then females and want the extra space.
For your UV get a tube light over a spiral as its harder on their eyes.
Handling wise, keep it to a minimum. Chams dont like being handled. If you want to get him a bit more use to people, hand feed him crickets while hes in the cage. When they hold one of their front arms out (like in a salute), it means they are defensive same with a open mouth or enlarged body. Keep the cage higher up, it will make them feel safer. Also try and look similar for the first while, chams can recognize their keepers but a change (hair cut, glasses) can upset them.