: . . . My 5-10 year plan is:

: 1) Build a tandem SOF
: 2) Build a S&G canoe
: 3) Build a S&G something else (sailing dinghy,
maybe)
: 4) Build a "real" sailboat

I think you'll be happier with a strip-built canoe than with an S&G one. While a lot of effort has been put into creating S&G kayak designs, not much has carried over into canoes. A lot of amateur kayak designs, and a few pro designs (like Nick's S&G Guillemot) are available as free offsets. There are maybe a dozen or two decent S&G canoe plans available. They tend to be sold as expensive, full size plans, and altering them is time consuming. I'm not sure why there is less development of good S&G canoes than kayaks. There are hundreds of designs for strip-built canoes, and tailoring any of them for personal reasons can be as simple as changing the placement of a building form.
N yet
If you haven't yet done so, take a look at the tandem kayak plans at www.clarkcraft.com. They are older designs and tend to be shorter and wider than many of the newer designs.

Just some thoughts for ya

PGJ