I think original PoE 1 it was just open up with a Blunderbuss; is that still the best way to do it?

Or does grabbing two fast weapons (pistols or wands?) and dual wielding for maximum attacks per second do a better job?

You can dual wield blunderbuss'

 

Does that answer your question?

I'm running a witch with whispers of the endless paths and draining whip, and he builds focus very fast. If I didn't love soul annihilation so much, I could spam cipher powers all day long.

Does Two Weapon Style stack together?

hunting bow is really good with its modal

Focus gained is based on damage dealt.  Guns offer burst (shoot at the start of battle to gain a large amount of focus).  Bows would give you better DPS.

 

PoE1 thread here: https://forums.obsidian.net/topic/87129-what-is-the-best-focus-gaining-ranged-weapon-for-a-cipher/

 

Multiclass contribute a lot to cipher focus generation since they have a lot of skills (such as swift strikes from monk) which help you build focus up a lot faster than before.