I would go with a solid state drive for the main drive and a 1 TB drive for storage. The case will come with fans (enough for now). the on-board video and audio will do for now but you may want to ugrade later. The i5 and i7 comes with a cooler that is pretty good. I would get two 8 (total 16 gigs) gig sticks of Ram so you can upgrade later.
Tiger Direct, Microcenter, and Newegg are your friends, they often have sales and deals. At Microcenter you can get a deal on the motherboard if you buy a processor.
I built one up and it was fun. Set aside a good area and get ESD wrist straps.
Sounds like a cool project for you and your son!
