If you use the small-image one, you'll probably be fine with a 2Gb card. If you want the large-image one, you'll need a 4 or 8Gb card. I recommend the former.

So far as I know, this is the only collection thus far. There are rumors that another one is coming, but I have no idea when.

It seems likely, though, that future wikipedia articles will eventually be tagged with "export defines", so that they can run monthly dumps for offline viewing. We're just not there yet.