Quoted:
I want the final product to be relatively light since it will get carried several miles at a time.
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Not going to happen with a 20.5" .308 Vepr. I know it's water under the bridge at this point, but you should have looked hard at a 16" .308 Saiga.
I own 20.5" and 23" .308 Veprs, as well as a 16" .308 Saiga. The Saiga handles like a Ferrari compared to the 20.5" Vepr. That was the whole reason for me buying the Saiga.
The Vepr starts out heavy (relatively speaking), and only gets heavier as you accessorize it.
For a scope mount, consider the RS AK-303 and AKR upper combo. Very lightweight, high quality, albeit somewhat pricey. You get what you pay for.
I like the MD Arms Molot grip (fills the hand really well), but the Hogue has a strong following as well.
A 1-4x or 1-6x variable would be a great choice. Relatively compact and lightweight (most times). Good up close and good further out at distance. I use a Leupold Mark AR Mod 1 1.5-4x20 (SPR Firedot reticle) on my .308 Saiga and like the power to weight ratio.
ETA: I'm not saying your Vepr won't make an acceptable carry rifle, that would be ridiculous. All I'm saying is that it will never be "light", even relatively speaking.