Yes, it can be used for a baby but it will be more difficult for you and it. You might consider a smaller cage until the baby is at least 4 months old. Makes it easier for the animal to find food and water, for you to find the animal.
Yes, 2(width)x2(depth)x4'(height) is large enough for an adult.
Panther care is quite similar to that for veileds. I keep panthers, feel free to peruse my blog for a collection of useful info. Make good use of the search function on this forum - lots of great info here.
these sites are also worth a look:
https://www.chameleonforums.com/blogs/sandrachameleon/56-chameleon-related-websites.html