I understand your feeling and motivation...
That being said, you haven't said what are your needs, and CPU/GPU/MB are yet untested, and you have some parts already... With the budget you mentioned, I'd perhaps go for 32gb RAM (otherwise - no, but for high-end stuff guess you could).
HDDs? Do you need a lot of cheap storage? At any rate, I'd include at least one - my preferences are Toshiba and Hitachi drives (normal), or WD Black (for high end) - all the Greens I had weren't great, I'd also skip Seagate Barracuda (more expensive series are fine). M2 may be fine, but perhaps you'd want some space to store its image...
The cooler is a tough decision, especially since AMD promises better auto-overclock with better cooling - for this, I'd really, really wait for some real benchmarks...
Hope this helps a bit in this, rather vague, situation. Anyway, I think you'll have some real-world tests available *before* you'd be able to actually build this rig, also the pricing is unknown and Vega is like several months wait...
