Re: Question about sail area
You're building a 12' boat. Why not build a 12' boat that performs much better all around and give it a flatter dinghy-type bottom and a fin keel? It's not like you're heading around Cape Horn. Design a good grid to spead the load and it will be plenty sturdy.
(I spent a lot of time and love on a full-keeled boat)
(If I was building a 12' boat I would stitch-and-glue plywood and get out sailing but maybe you're really into woodworking or want the experience)