Minecraft costs USD $26.95, so I'm assuming that amount and maybe a few dollars extra will allow you to purchase a Minecraft Gift card
I would say not much, because Minecraft is mostly pixelated.
NO
it might be your visa card try email visa and/or minecraft for suport.
Yes, you can buy Minecraft with a Visa card
No.
NO
You have 256mb there are no 258mb card but 256mb will do nicely
Nope
yes
Minecraft currently costs $26.95 US dollars. You will need a PayPal, or debit card/credit card. Unfortunatly, if you are 11... You are not legally alowed to own a Credit Card (Assuming you live in the US) so ask your mom to get it, or go to your local store and hope they are selling gift cards.
A video card that supports OpenGL. Nothing too fancy.