: Weight would be the only consideration. . .

Please, also consider pleasure, leisure, athletics and esthetics.
Make it fun, as well as functional.
Splurge a little on the weight and built in the features you want. A fiberglass kayak is 70 pounds. It makes little difference if yours is 35 or 50 pounds. It will still be one heck of a lot lighter than anyone elses boat.

and I won't be going overboard with
: fittings - I'll leave the walnut and glass drinks cabinet out of this
: build ;-)

Last year I had extra black walnut and I sent out free pieces to anyone who would contribute postage. It looks beautiful and a slice forveneer weighs an ounce. A two-pound liquor cabinet weighs less than the bottle you'll put in it--and NO ONE has a walnut liquor cabinet in their fibergass or kevlar boat! Why deny yourself the pleasures inherent in a small yacht.
Don't worry about an ice chest. When Captain Morgan and Johnnie Walker appear you'll find someone with ice who wants to be introduced.

Enjoy the experience. Drink and paddle responsibly.

PGJ