Similar to epoxy, it really depends upon how effecient you are with your coats and how much wastage there is after each coat.  For my Skerry, I did 4 coats schooner and 2 coats satin varnish on the interior and 2 coats primer and 3 coats brightside on the exterior.  I also varnished the mast, spars, daggerboard, rudder assembly, rails, inwales with 5 coats schooner.  I painted the bottom half of the rudder assembly.

The Skerry I assume has less volume but I am also not a particularly neat painter and I probably put coats on too thick sometimes.  I had minimal wastage after each coat.  That being said, I used 1 1/4 quarts of schooner, 2/3 quart satin varnish, 1/2 quart primer and 1 1/4 quarts brightside.  The remaining varnish I won't bother keeping since it doesn't keep that well but the paint is always useful to have as I have already done a couple touch ups this fall.

Scott

   I went through the better part of 2 quarts of Brightsides on my Skerry, partly because I sanded a lot off to correct boo boos.  The better your surface prep, the less paint you will need, though.  I used the high build primer and I'm not sure I'd use it again.  I'd spend more time on surface prep, even to the point of an extra coat of epoxy or so for more fairing and sanding.  My finish coat seems softer than I remember Brightsides being, and I wonder if the chalky nature of the primer is to blame.  

BTW, I'd get one of CLC's StopLoss bag kits.  They work well for varnish and paint so you have leftovers for the inevitable repairs and touchups.