Yes you can. But you need to have it registered online before hand. ( Ex. My visa giftcard came from Wal-Mart, so I had to go to the website and register it. )

Yes you can buy things online with a visa giftcard

yes but it won't work if you use over the limit. if its a gift card for 50 dollars, you have to buy 50 dollars or less. most places won't let you use s second card to help out.

Go to my 999 store.

Yes :-)