You did not indicate the extent of the deck work. Are you removing all chainplates, winches...anything with thru-deck attachments??
First the issue of sanded surfaces. Your prep will not extend past the gelcoat layer. The sanded surfaces will not be anymore susceptible to moisture migration than the unsanded surface. But, as you trudge about the deck in the winter months, will you be tracking dirts and oils and, worst of all, silicon about the deck. The sanded surfaces will be more permeable to these surface cantaminants. Prior to the Awlgrip, you need a solvent wash, anyways.
Fillers - Assuming you will be using epoxy with micro fibers/balloons? Epoxy curing below 60F is vitually non existant! You will have to babysit the curing a bit with heat to get an appreciable cure. If you use poly or vinyl ester resin systems in the filler you can adjust catalyst rates for cures at nearly any temps.
With all this effort, you might consider pulling all the deck hardware, over drilling holes and re-casting with epoxy to seal exposure of the wood core areas to moisture/rot.
I agree, you can get a one foot job with these two part LP systems, but surface prep is 90% of the job!! I used Interlux on the spars. People still think it is better than the best spray booth job!!
You might as well get started!!