Hardware requirements for graphic design

Hardware requirements for graphic design

I'm helping a friend build a computer to be used for graphic design.
Photoshop, Illustrator, that sort of thing. Probably not 3d graphics or
video, but I imagine it'd be nice if it could handle that. I'm not really
a graphics design person but I've built several of my own systems for
gaming. Ideally he'd just buy a Mac for the job, but due to budgets he's
going with a desktop PC.
My understanding (and this could be wrong) is that gaming and graphics
design have a lot of overlap when it comes to hardware. i.e. a good system
for one is most likely a good system for the other. I want to make sure
this isn't a flawed assumption before I start helping him though. I'm
hoping someone else here can tell me what I should look for, not
specifically (like XXX model), but in general (Video cards are just as
important, make sure it supports YYY).
Is there any specific features I want to make sure the video card
supports? Such as DirectX versions or shader models?
In general I choose nVidia for games, and Radion for pure speed (crypto
and the like), not to get into a brand debate, but I find they both have
different strengths. Is one brand or the other better for graphics design?
I've read about people building PC's with Mac compatible hardware. I was
under the impression you couldn't install OSX on just anything (I'm not a
Mac person). How true is this? Anyone have a guide or something? Is this
something I should be concerned with?
I assume RAM and CPU are just as important as in gaming. Are there any
other hardware components I should look at? Disk access speed?
Again, budget is a concern, so all of this won't be perfect, but once I
get an idea of what is vital, what is important, and what is just a nice
thing to have I can prioritize and pick the parts myself. Still, if anyone
has specific suggestions I wouldn't mind hearing them.
Thanks