: However, the spacing between cross sections in the bow seems quite
: big, up to 26". Should I add a couple of extra cross
: sections between 2/3 and 3/4?

I guess no, you won't need it in the bow. There is an old boat from Yost (fap 15) that looks very similar (I mean the bow below waterline) and Tom used 4 (2 front+2 rear) sections only and it seams to be stiff enough to stand a trip in Niger.
http://tinyurl.com/aprx7y7
The f1's stern is sure more critical as it has been designed to surf huge waves. So if you really want to add an extra section, you probably want to add it in the stern than in the bow.

P.S.:
How did you get the right offsets for the F1 cross sections?