epoxy is a great adhesive and an excellant resin for laminating glass,
if you are glassing, the benefits over polyester or vinyl ester are worth the xtra cost imo.
its generally not a good paint unless sold as such with the associated surfactants, pigments and uv inhibiters required to make it a quality user friendly exterior coating.
that usually makes it a lot more expensive than suitable alternatives.
Resin Research sells a surfboard laminatng epoxy that claims to address all of the above failings i have mentioned . i plan on using it some day but haven't yet.
i the meantime there are a lot of plywood boats made over the years that were only painted or varnished with long lasting results. using nothing will probably allow the plank to twist and warp over time as it repeatidly soaks and drys. ( btw, a tried and true method to put rocker into a plank). Structurally i bet it will last all summer (or two) before anything starts to delam.
i am not a fan of glassing over paint. if you've chosen the epoxy as a sealer or adhesive the paint will limit your ability to do either. if you chosen the epoxy as another layer of paint....well you know already how i feel about that
my approach to most 'engineering' type projects is:
Good, Fast, Cheap.....Pick any 2
you've already downselected for fast and cheap.
the added expense of epoxy for a varnish really adds no value over the alternatives.
if you really have your heart set on glassing (no biggy , this is a good place to learn those skills)
But i would practice a bit to avoid wasting all those liquid dollars before they actaully wet out the glass it was intended for.
mix a small amount of resin equal to the weight of the glass you are using and try to get it completely wet out....that should be your goal.
its easy to squeegee 3 of 4 times that weight of resin into the wood with limited structural benefit.
despite all my predictions of doom, much of what you are proposing is common practice for small boat building projects. I'm sure the gougeon brothers of west systems just wanted to sell epoxy , but it can be an easy way to make a strong, light boat.
you'll find lots of good references from the strip-built or stitch 'n glue kayak folks for both glassing and varnishing.