I've only used the A8K fella and the stock heatsink wasn't that bad at all. I did whack on a value heatsink to a few builds but that was to OC the CPU and IGP.
I'd avoid the Asrock ITX mobos, there were reports of them burning out. That's why I went with the MSI. It has USB3 rear ports and a internal header, I do believe it has bluetooth and wifi as well (Spec sheet
HERE)
For your boys build the A8K again makes sense but maybe use 8GB of 2133Mhz (or faster) RAM to help the IGP for gaming. You can always drop in a dedicated GPU later or hand down your old one perhaps if you upgrade. The A10K has the best IGP but that's down to you how you want to balance things out for him, if you would add a GPU much later the A8 makes a good compromise.