I have yet to receive the figures but looking for advice on how to paint these figs

a: black base coat with metal (sliver) drybrush

b: silver base followed by black washes

For me everything is undercoated black

Yep, I'd black undercoat them too. I tend not to drybrush but to block in colours, wash the figure with inks or with Army Painter quickshades and then pick out highlights.

If you google Norman or Viking or Early Medieval re-enactors and look at photos of people wearing actual mail, it appears to be various shades of grey. Unpainted helmets look a lot shinier.

I find the best way to get this look is to undercoat in black. Mail areas I dry brush in grey then a very light dry brush in oily steel. Helmets I just paint in oily steel.