Nice box.
The power supply is quite easy, remove the 2 or 4 screws holding the old one, pull all the plugs and remove. Slide new one in, screw in place, connect the cables you need. They should all be labeled, and if not, most of the plugs are sized to fit each device. Looks like you will have a fun time hiding the extra cables.
Most of those cable with the this black ends are for SATA, so stash them first, since you don't need them, then untangle the rest.
Don't forget the second MB power supply plug - 4 wire - above your VC.
You don't have any RAM?