winter project, insight requested

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mcgillicuddy, keep on rambling. like the ideas. going very simple, never built a boat before. want to keep as light as possible. 3/4" marine ply bottom, 1x4 vertical supports (rib style, but not U shaped), .25" mahogany plywood around the sides, mahogany 1x4 and ____ on the top, partially enclosed like a kayak but set up as a rowing scull. when i mentioned light, i meant color wise. i was thinking about using one wood for all the supports, and the trim around the gunnels, and the mahogany running the long ways on the top (think, older runabout style). next question: will i have to glass the whole outside, or can i just do the bottom and 6" up? that is how the "template" i got was done, but they also used drywall screws to hold it together and the plywood sides were warped and cracking everywhere...i want to finish the whole inside w/ spar urethane, not fiberglass. also, should i biscuit join the 1x4 or just use a glue joint? ive heard varying opinions on this...lastly, im going to look at white oak today. or i may just go all mahogany, last time i got it surfaced 4/4 for right around $5 a board foot, which is super good price.