TJ Hooker :
Not sure if it's officially supported, but I believe you can crossfire a 470/570 with a 480/580. Crossfire requirements are more lax than SLI, I believe the cards only need to have the same GPU (Polaris 10, aka Ellesmere in this case).
But as said above, even if you can, doesn't mean you should.
This is possibly true, but keep in mind that the combos will run at the speed of the slower device. You still have the heat/power (and dreaded micro-stutter) issues associated with multi-GPU configs. It should also be noted that some games don't support these configs.
Heck, you might even be able to do the 470/580 combo, but it would be like having 2 470s. Not sure worth the hassle. Rather, I would sell the 470 and get a stronger single GPU solution as noted earlier.