Sometimes when I'm developing a new stitch and glue boat, or kayak, I use heavy card stock, or very light cardboard, to make "small" models. I've never made a full size model. Even if one is using a design program it's probably a good idea to make some kind of model before attempting the full size boat. I also size my boat according to efficent use of plywood sheets....such as 16', 20', 24', and so on to minimize joints. The actual size of the boat would be slightly shorter due to the curve of the sides. V bottom, flared sides, full bow and stern, low sheer to help with paddle clearance, arched deck for storage, large cockpit, large hatches. I would consider some moderate rocker. I once built a wide, light, 16' kayak with straight bow and stern, arched bottom and no rocker. It was very fast, but the first time I tried it I ran into the bank because I wasn't prepared for how hard it would be to turn. Took some getting use to. Your length is probably ok, though I tend to go shorter...others will probably say much narrower. You could probably go a little narrower...maybe down to 28". In many respects what you are trying to design is a hard chine, covered canoe. I'm no expert...just throwing out a few comments, but I think what you want to do is possible. I would do a lot more research and view other comments that are sure to come. Nick Schade has written some good stuff on hull design on this site. Check that out. It will be interesting to see other comments you get. You probably won't find any plans for a kayak of that size/width. Maybe some really good designer will be challenged by the possibilities and help you out. If I could...I would...but I'm one of these guys who just keeps trying all kinds of weird things until something works. Have fun.