Hardware specs needed

Recording won't be an issue...
Mixing is where the slow CPU clock-speed would be an issue.

Mesh
After speaking with him, he's decided to get a new machine (PC) . He's also planning on doing some very light midi stuff, but mostly audio (as above). 
Although I'm just a novice/hobbyist, I've offered to help him build one as he's not comfortable doing it on his own.
 
What are some good options to build a machine for under $1000 budget?
 
I know Newegg, PC Partpicker, Micro center, Amazon etc...have the deals, but some suggestions on the Motherboard (full ATX?), CPU (AMD or Intel), Power Supply etc... to do light DAW work would be greatly appreciated.
 
  

For a decent budget build for light use probably go with a microATX board (9.6 × 9.6 in) and the best power supply you can afford. 
 
The main limitation with microATX is you usually only get 1 PCIe 16x slot (for optional GPU), and 2 PCIe 1x slots for expansion cards.  And probably only 2 RAM slots instead of 4.  If these limitations may be an issue down the road, go with full ATX (12 × 9.6 in). Also consider a full ATX case for the extra room to maneuver inside during the build.  But performance wise, there should be no difference with same chipset between ATX and microATX.
 
For light DAW work a combo deal with an AMD CPU and mobo would be most budget friendly.  I have always used Intel, but that is just my preference.  But some folks around here are happy with their AMD rigs, so that is a personal decision.  I suspect it may not really matter until you start comparing high-end rigs and latency specs that you may run into any performance issues with Intel vs. AMD.
 
I suspect that you could build a decent machine for way under $1000, including 16GB RAM and SSD. See PC Partpicker for that estimate. 
 
Good luck!  Sounds like a fun project.

Would that PSU be a bit overkill for the system above?