Dave, Without changing the glass layup the easiest thing to do to not make the kayak heavier is to use the least amount of epoxy necessary to bond or seal the materials. For fillets that can be 1/2" wide if you don't round off the outside too much. Use tape to mask the width of the fillet . When glassing squeegee off the extra epoxy that makes the glass vary in thickness. Warm epoxy and workshop will help a lot, 70 degrees. Thin coats of anything are easier to control. Wipe up drips.
Don't get anal about weight, a 17ft kayak made of 4mm ply,6oz glass and 9oz tape is going to weigh around 40-45lbs with hardware. It can weigh more if epoxy is applied messily, it can't weigh much less unless you change the glassing or leave out a few items, like bulkheads, hatches, tape, etc.
Be neat, don't be in a hurry, don't worry.