Tim,
I don't know how any ply boats are in that fleet.
I would guess that around 10% would be timber.
This is just a guess from what I've seen over the years.
As far as kayaks go-
I thought I'd build some kayaks during the winter and got some plans from one of the US companies that also sells kits.

Pretty easy to build from the plans. It is easier than tortured ply but uses/develops many of the same skills.
I'll attach a pic. Anyone thinking of building a cat and does not have the confidence to jump straight in could try a kayak first.

Regards,
Phill

Attached Files
94736-kayaks.jpg (245 downloads)

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!