The number of layers depends on the boat design. If the glass is meant to be part of a structural composite, the designer should have completely specified the lamination schedule. If there's no specifications it's probably just for abrasion protection. In that case, a single layer should be fine. If you're going to be beaching on rocks and gravel, a second layer on the areas that get the most wear would be a good idea.

From data in the System 3 Epoxy book,that should take about 1/3 gallon of mixed resin and hardener. That assumes a skilled worker getting an optimum glass/resin ratio, no waste, a softwood plywood and a saturation coat before the actual glassing. It also includes the epoxy required to fill the weave.

Based on your questions, this is your first time playing with glass and epoxy, so you should probably allow a good 15% for waste, as well as a bit more for a less than optimum glass/resin ratio. In addition, you'll be needing epoxy for the fillets and tape on the seams. I'd say taking all that into account you should get one of the1.5 gallon kits (1 gallon resin, 1/2 gallon hardener).

Have fun,

Laszlo