If tried a a juvenile, a minor may be committed to the custody of the state until they become an adult. That could be a very long time.
Federal prison time, fine.
packing
Indiana does not have gun registration. If you're carrying your firearm in the legal and prescribed manner, there is no requirement for it to be registered.
It's illegal for a minor to buy a gun anywhere in the US.
No.
Yes
You will have to go to court.
It depends on where you are carrying it (local laws), what you are doing with it (brandishing or threatening) and whether you are a law enforcement officer. If you were in possession of a stun gun while committing a crime, you will probably get time tacked onto your sentence.
Just as much as if you use a real gun.
Laws on this vary by jurisdiction.
packing or loaded
only unconcealed