Don will need an i7 processor, with at least 8GB of RAM and plenty of storage. Leo thinks that he should buy instead of build. Building is great for hobbyists, but it's better to "spec out" a machine at Dell or Apple. Then if he has issues with his computer, he'll be able to get support.
Having a Solid State Drive (SSD) as his master boot drive with an additional 2TB drive for storage would be best. He should also get a large monitor, or if he can afford it, two side-by-side 27" monitors since screen real-estate will be important for what he wants to do.