Does Twains arc proc mana/life steal?

I have a few questions about how archer works. One of them is in the title, "does twain's arc proc mana/life steal?"
Here's a few more:
When arrow shield/guardian angels loses its last charge and arrow rain activates, what happens to focus? Does your focus just stay? Does it stay only if at least one of the arrow rain arrows hits? Does it only stay if ALL of the arrows hit?
How viable is a tripleshot homingshots focus tierstack build? Do the homing shots work wonders and make it so your tripleshots almost never miss, preserving your precious focus, or do the homing shots not work well enough at all and it's near impossible to maintain any focus while using tripleshots? I want to know if I should use triple shots in focus tierstack builds or not.
That's all my questions I really do hope that twain's arc procs mana/life steal and arrow rain doesn't kill focus and triple shots are viable in focus tierstack builds but if not that's ok I'll find some way to make do.