Cobra Lash + Endless Munition (+2 proj) = 3 projectiles out per attack?

Haven't played Cobra Lash much, so sorry for the somewhat noob question, but if I get the +2 projectiles from Deadeye, does that mean I shoot 3 projectiles per attack? (is it same for LMP/GMP?)

Yes, +2 proj from deadeye looks similar to LMP. It stacks with LMP or GMP.

You will not be able to hit a single target with more than one proj per attack unless (I think) it chains into them from another source like an additional mob or hydrosphere.