Yes you can but firstly you need Internet . Go to wii shop channel click on virtual con sol and search for Mario 64 . you also need 1000 Nintendo or wii points witch will cost £7. If you don't have...
Yes
For virtual console through the wii shop channel. there is no "disc" or "wiiware" form of it.
It would usually save when you come out of a painting for the DS so it would probably work like that.It can also save when you decide to quit.
I'm not sure but you can buy the original on virtual console.