Yes.
No, you do not need a gun license to buy magazines.
Far too many (thousands) to list here- license requirements vary from one place to another. We cannot answer without knowing your country or state.
yes
No it's not necessary.
A gun shop.
If you are 21 and have no criminal record there is no requirement to have a carry license however you do need one is you wish to carry concealed.
No, it is not legal to purchase gun magazines without a license in California.
Yes
try gun shops and gun shows.
Gun shop, gun shows, internet auction.
No.
no