yes
You should be able to buy it at most stores that sell 3DS Games such as Gamestop, EB Games, Walmart, Best Buy and Future Shop.
The eShop for the Nintendo 3DS is out already.
Yes
no
no, maybe in the future.
Visit the Future Shop website and see for yourself (the current models are the same price EVERYWHERE, BTW).
June 6
Not at the moment but there might be in the future. there is a Zelda Ocarina Of Time on 3DS though.
It isn't on the 3DS but it may be in the Nintendo eShop (a 3DS game shop that will be released in the June 6th update) so keep your fingers crossed!
On the 3ds shop, you are able to buy and download older games. That work for the buttons on the 3ds of course.
Yes, you can use a prepaid card to add money on the 3DS shop. The card will work as long as there is money avaible.