I for sure wouldn't have made it as wide. That is, I think. Cunningham offers some advice on a reasonable range of widths and I went wide. If I make a second I'll stick with the baseline width, and we'll see.

I would have built in some sort of floor boards. For as concerned as I was about making too narrow (unstable) a craft, the only time I've tipped the thing is in a few inches of water, trying to extract myself and getting snagged by a rib! Pretty rough on the ego. There's some concern that floor boards can raise your center of gravity- but I don't think I'd extend them to the seat. It's my legs and heels that would appreciate the smooth surface. I tried a piece of yoga mat as a retrofit solution, but it was a hassle and didn't really work.

I'd have slid the foot rest beam forward a couple of inches. I'm sure it's at least in part a sign that I need to be more flexible, but I just don't find it comfortable. Partly the placement (pulls my feet back close to 90 degrees) and more so that it puts pressure on my toes instead of, say, the arch of my foot or heel.

And for what it's worth-I'm no speed demon and I built mine in under two months. I can't say for certain, but it was likely one weekend day per week.

Good luck!
Patrick