I’m not a big fan of Two Fang… What class mod are you using? If a Leg Sniper, I’d put one point in Kill Confirmed as why not. You are right that Precision can help with shotgun accuracy and most of Zer0’s sniper buffs apply to shotguns too. I’d rather have Killing Blow than Iron Hand, especially with Execute, but if you never remember to melee anything, than it doesn’t help much. Another idea would be to take some points out of Precisi0n (just have one and then you get 5 with the class mod) and one from Optics (not much diff at 4/5 or 5/5) and put 1 into Kill Confirmed like I said and the rest into Unf0rseen which can pick up stray kills for you or at least weaken enemies.
Two Fang , Velocity, and Unforseen are all personal preference skills. Two Fang can give you an extra bullet but throw off your aim. Velocity is more damage, but makes it take a greater distance for the bullet split on the Lyuda, Pimpernel, and Bekah. Unforseen is more damage and way of clearing enemy shields (and outright killing trash), but a lot of people think it’s pretty meh.
It’s one of those you need to try for yourself and see. Take some runs in a big mobbing area with some space like Lynchwood or Sawtooth (or Friendship Gulag for loaders, Wildlife Preserve for everything).
Another thing is to look at your build with a Leg Hunter or Spy class mod (you want the blue one that boosts Unforseen and Ambush) instead of a Leg Sniper. Leg Hunter is great with Innervate for surviveability plus the cooldown bonus. Boosted Unforseen can be very powerful and you already know how strong Ambush is.