After some months of work I finished the build, and was able to launch my Guillemot today. I named it "zen" - to make one is more important than to have one. The seat I use is a wooden racing kayak seat made by GEES in England - but I have already the plans from Nick Schade to build my own :-).
The boat is really excellent, and its very fast, too. I think I'll made a second one soon.