If you buy Core you get all streach goals - so most of figures. If you want to get X-Men figures from their Core Box, you have to buy both Core and X-Men Core Box. If you want Guardians of the Galaxy you have to buy it additionally.
If you want to buy 1 or two figures to paint or have them, next year, when the game is out, there's a chance that someone will be selling everything separately (like they do with Marvel United).