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?
Check the Vega threads , it is very easy to make a batch file to disable and enable the cards on startup, HBCC isnt the factor boosting the Hash rate , it is a driver bug where you need to disable and enable the GPU and that is exactly what HBCC does . ,Better use a Mobo with Built in GPU and use a Dummy plug for screen on all the time . the only thing i am having problem with is that with every crash i need to re-adjust wattman settings .