The replays I got for a microbootlegger was - 6 oz typical, 4 oz if you want.
For strips 1/4" typical, 3/16" is becoming more common, 1/8 is done by Nick (with a carbon layup inside).

Thinner cloth will take less epoxy no matter what. Assuming you don't put more than 2 fill coats. Each extra will add weight, but how much you sand off matters - but is not controllable.

You don't need anything but glass unless you are in the Nick Shade league (1/8" strips).

Graphite of the same weight (Ex., 6oz, will be thicker) will require more epoxy to wet out, but no more to a fill coats (theoretically).

For min weight that assumes you use a majority of cedar - typically the lowest density practical.

Last thing, for the coaming I have not used glass on 6 boats, just epoxy.
On the last I decided to use 2oz to make it "better". 2oz is too fine to handle for me, there are some bubbled areas where it will get completely sanded off to get it level.
No glass should be lighter, its been strong enough for me in the past. My coamings were molded with epoxy for adhesive.

How much will the seat, foot pegs (and rudder or skeg if you are inclined that way), deck ropes, and hatch hardware weight?

Good luck and keep the pictures coming. :)