Wish I could help you on the hardware side but there’s so many CPU choices out there. As for memory, yes, good idea. I splurged on 32 Gb when I bought my rig (3+ years ago) knowing that would be necessary eventually. 16 I would think is a practical minimum. DCS will use all it can get its hands on.
What @Cib and @komemiute say about Windows.
As for getting a 2070, if you can find them, I can only comment on my recent experience trying to upgrade my V-card: I don’t have the power supply necessary to support anything over a 1080Ti it seems. A chain reaction in my wallet begins here.
As you’ve noticed, a new system seems a good idea. However I’ve come to the conclusion that DCS (I only play DCS and sometimes X-plane) isn’t optimized well enough to justify the expense: 'Bang for the buck" is too low. So I end up, essentially, playing DCS just like X-Plane - my system, and I’d argue there is no system, can’t handle a full-blown war going on. So I do a lot of what amounts to “low intensity” conflict-like scenarios. Keeps me off the streets 
Now, this is all based on reviews of the latest, greatest, V-Cards and VR headsets (along with newer gen CPU’s), not first hand experience of course. Still watching though as some reviewers may not have the savvy to get the most out of their systems; they might have inefficient setups. More reviews should shine more light on this.
Tweaking shouldn’t be that necessary with these new powerful rigs but, well…