4gb is sufficient. the HBCC issue, you can just disable and reenable cards in device manager. No need to toggle HBCC.
I only have 2 rigs of vega and they work with 8gb. (bought a ton of 4gb sticks so most my rigs run 2 sticks)
How often is this kind of maintenance to re-enable HBCC required?
Never with your 8GB?