You will have to state whether it is a rifle or handgun to get an answer.
No.
Only NFA regulated items. For a typical rifle or shotgun, no.
You will need to define assault rifle, and where you live. A TRUE assault rifle is a machine gun, and transfers of them are tightly regulated by the Federal government. What most people CALL an assault rifle is nothing but a semi-automatic rifle, and in most of the US, does not require a license to possess.
You don't need a gun license if you are 25 but if your under 25 you do need a gun license
No, you do not need a gun license to buy magazines.
You never need a license to have an Airsoft gun.
No, you do not need a license to purchase gun magazines in most states in the United States.
no, if your gun is below the legal muzzle velocity which is 12 ft/p/lb [12 feet per pound of force]
To get a gun license you would need to go into a gun store in the town you live in and ask for the information you need.
No.
yes