: 2. What type/size of materials would anyone recommend for the forms &
: stringers? (I would like to go ultra-light, but I weigh 200lbs and may end
: up using it in some rough conditions, but mostly day trips in small
: lakes). I thought of using very thin plywood reinforced with strips of
: glass/carbon.

I would think you'd have to use plywood for the forms. Perhaps 3/8" would be sufficient. Coat it with varnish or epoxy (especially on the bottom half) to minimize water penetration.

The stringers could be pine, fir, spruce or even cedar.

: 3. If I were to use a fairly dark colored paint, could I use 18g galv. brad
: nails or screws to secure the stringers to these forms without lashing?

I'd lash it. Lashing allows the boat to flex a bit. If you're using thin ply for the forms, you won't have enough material to nail into, anyway.

: 4. The Guillemot S&G forms are easy to use, because of the hard chines. Would
: it be possible to do the same exact thing with any kayak design?

Sure.

: How would you mark the position of the stringers on a more rounded design?
: Would you have more stringers?

Everywhere there is a significant change in the curvature of the hull, you'll need another stringer.

: I'm thinking about a skinned Little Auk, is that
: possible?

I don't see why not.

: 5. How difficult is it to stitch the skin on a skin-on-frame kayak?

I found that it's not so much difficult, as it is time consuming. Depending on the size of your boat and the sewing method, it can take 6-12 hours to stitch it.