I don't have any experience with designing something that long but I'd stick to your own design principles to get what you want. That said here are my thoughts.
With a 10 foot boat you'll probably end up with more rocker in the stern than 2". My boats are pretty flat and at 7 feet they have 2 to 3 inches.
A 21" width although fast to paddle in is hard to design around not mention unstable. You'll want your side walls angled in enough so they don't drag when you're on edge. So when you angle in from rail to cockpit area you'll end up with a petty vertical side wall at 21 inches. Also a wide boat will plane out at a slower speed thus making it catch a wave easier although slower to paddle.
Anyway stick to your own ideas and don't copy others too much and you'll get the boat you want...................................Gary