My understanding is that AM3/+ is a socket that doesn't have anywhere left to go. I actually really like AMD, but if he's only gaming he might be better served by a dual-core i3-2100 (LGA 1155) and upgrading down the line if he wants/needs to. That said, I doubt there's anything the FX-4100 can't do gaming-wise right now, and it will come in handy if he ever does
do something multiple-core intensive.
I don't know anything about hec, but I recently decided to go with a well reviewed XFX PSU
. It's essentially made by Seasonic, which is tops when it comes to PSUs. I don't think 750w is necessary for a single GPU system--even 650w should be more than enough.
It would be nice to have a 120GB SSD, but that would be tough on your budget.
The resources I used a couple of months ago are here
I would assume all the cables come supplied (or they did 7+ years ago).
Most likely, but the motherboard specs should tell you.
We were thinking of salvaging the DVD drive from his old PC as well, but not sure of compatibility.
If it's IDE, it won't be compatible with the motherboard you've chosen. Neither will any old HDs. A new DVD-RW can be had for $15 or $20 though.