Females in my opinion are less aggressive than males. They are not harder to keep the only big difference is you need a lay bin for her once she's sexually mature. Right now she's a baby and will need to each as much as she can to grow but once she's an adult you don't need to feed to much so...
I spend a lot of my evenings just sitting in my reptile room. All of my chameleons expect food from me and are usually begging. When someone else comes down into my reptile room my chameleons will go hide except my female panther... she poofs up all angry like.
It could be possible that it was a bite from a sibling that did the damage. Might need antibiotics. Did you get this guy from a petstore or a breeder? Do you know if he was being kept with others?
In my opinion this is probably due to not having enough calcium while growing. Now that he is in your care it's best to make sure his supplementation schedule is on point. You did not mention weather or not you are supplementing or gutloading your insects.
That terrarium will not be suitable as he grows. There's definitely a lot your going to have to upgrade in order for your chameleon to have a long healthy life.
Well he seems to me like he's defending his territory from his reflection. And considering how his reflection doesn't back down when he puffs up he ups his game to head butts.