I showed 1 RX 580 8Gb card - it's enough. Other cards looks similiar.
This card running stable for weeks with this settings without any incorrect share. It's Sapphire RX580 8Gb Nitro+ SE.
Core and mvddc voltages for each card can be individual and needs time to pickup best values for each.
All cards have hynix MJR memory.
Power consumption from the wall maybe a bit higher, but not so much. If chip consumpes 95-96W summary would about 20-25W more. So it 115-120W. My Corsair PU shows such increase when I run 1 card.

And don't forget about REF setting in AMD Memory Tweak tool. For each card this value differs. For card on screen it 64.