On shooting multiple arrows at once:
Kromm lays it all out in glorious detail in this thread:
http://forums.sjgames.com/showthread...48#post2392248
It's for
DF, but of course can be dropped into
DFRPG.
From there, the question for this thread becomes "So what are the effects of crit success on the Fast-Draw component of the feat?"
Off the top of my head, maybe this: On a crit success with Fast-Draw (Arrow), the PC has the
option of grabbing one more arrow than attempted: two arrows if the intent was to draw one, three if the intent was to draw two, etc.
The PC who fortuitously grabbed (say) two arrows instead of one could then choose to shoot both at once (see link above). Or, since that's a difficult task, the PC could shoot one, while the other one stays deftly held in the draw hand, meaning no need for Fast-Draw on the following turn.
Sounds workable to me. Of course, it suggests that anyone could intentionally load up the draw hand with multiple arrows in advance, taking a bit of time to do what the above Fast-Draw crit success accomplishes, so you can start the fight with two or three or four single shots in succession, requiring no Fast-Draw. There should perhaps be a TH penalty for firing while holding on to additional arrows, but the video restlessgriffin linked suggests that it's definitely a thing you can do.
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All that said, there's a beauty in keeping things simple for
DFRPG. I've no argument with a GM who says crit success of Fast-Draw (Arrow) has no special effect.