1. If you want to function and work as well as the legit version then you have to buy it. There was kid who had the bootleg that lived down the hall from me my freshman year of college some filters were screwy and his transformations would make his computer shut down and bunch of other random things.
2.C3 is the most up to date version. its not mac only but its fact, that adobe software runs faster and better on Macs, because of their ability to render graphics is far superior and they come out of the box far more color correct than an pc. Also macs come standard with decent amount of good fonts, while i've added quite a few more and added most of families of good fonts, pc's come standard with terrible fonts most of which are knockoffs of good ones so unless you buy or steal (which I dont recomend, some kid on here's futura was screw and I'd be willing to be its cause its bootleg) you're stuck with bad fonts.
3. It does run alot, but most people on niketalk would probably be set with photoshop elements which has most of the basic features and runs about $99.