Halik, go with "b" the barebones but nearly complete box, especially if this is your first Mac. Apple does some funny things with their hardware, and while it is indeed possible to hack something together, it's usually not worth it. Especially if you want to run OS X which is very picky about what components it is compatible with.
You've obviously been looking at prices so I probably don't need to tell you that many peripherals are going to be more expensive than their Wintel counterparts. Take the Mac GeForce you're looking for. It will probably cost you 1.5x what the PC equivalent would cost.
As for the OS X hardware compatibility, I'll just give you a quick example. I have a USB Que CDRW that I bought a couple years ago. It's obviously pre-OS X, but Que as a vendor has always been a Mac supporter. With OS X my CDRW is now useless. Apple refuses to support it, and Que can't write OS X drivers for it. Since you're looking at a geforce card, be sure to read in mac forums like
MacNN and
macfixit. I've read complaints about OS X and GF3.
Personally, OS X is the reason I've completely given up with the Mac. I'm a professional graphic designer who has used the Mac since it was introduced, but OS X does nothing but make me mad. It's NeXT with a Mac face. It doesn't feel like a Mac, it doesn't work like a Mac, and Apple is screwing customers of supposedly supported hardware. (I.E. my old Mac that can do some QuickTime dev with OS 9 will never be able to with OS X because Apple has decided they won't enable the hardware acceleration on that machine with their "upgrade" OS.) If you like that, then great, more power to you. It's just not for me.
Good luck with your design stuff, whatever you decide to do. There isn't a "right" choice, just money to spend.