Dear Hellmuht - that looks absolutely stunning. I have also started on a sampan in anticipation and preparation of other Chinese modeling subjects - be they junks or sampans. My research has shown that wood choice was down to the individual shipwright and depended mostly on the area where construction took place. It does seem though that cedar wood was a variety widely chosen with fir wood also used in the construction. Fujian (Foochow) pine was mostly used on junks and sampans built in that area.
I agree with you that those ships were not richly ornamented. Interestingly, Shicheng Model Company (based in Huangzhou, China) released a model of the Huaguangjio Reef I, also known as the Huaguang Reef I a while ago, which is apparently based on an extremely well-researched model found in the Museum of the South Seas in Hainan.
View attachment 243043
This one features the almost obligatory Phoenix on the transom.
View attachment 243044
And indeed some decorations and color - including the "Guiding Eye". In both cases though, you can see that your interpretation of the clinker planking is spot-on!
I can't wait for you to continue.