Lens & gear advice for wedding in Siberia

Look up the Lumiquest at B&H (or your favorite shop), it's a softbox (8"x9") that fits on your 580; combine it with a coiled ttl cord and you can hand hold it to the left or above (or ask your wife to hold it to the right) to get a different lighting angle and still shoot TTL flash.

There's also a set with color gels and a snoot at something like 80$ you could like.

If you think it's too big, they also have smaller softboxes but these will give you harsher light.

Alternative to the TTL cord, but a lot more expensive, is to go for the PocketWizzard FlexTT5/MiniTT1 combo; that way you're not limited by the length of the cord and still get to use TTL.

As for the QuickFlip, I never used one, so no intelligent comments possible from my side.

I wouldn't go for a 2 flash set-up (you're not the main photog, too much hassle, and you're not used to it), and would even consider flash optional ; my personal shooting style would be to go available light B/W to complement/differentiate the main photog.