I seem to recall that the plywood/epoxy thing doesn't work great in high humidity areas? Can't find it now, but I think there was a southeast asian build where the plywood picked up moisture and didn't glue up very well. So I would keep that in mind, hope others chime in with the correct info. What I recall was that building stitch-and-glue in high humidity caused issues due to plywood picking up moisture...
Based on 'fishing rivers and also going offshore', I came to the same conclusion you did. I also had some background with boats (much less than you!) but ultimately came around to following the book about as closely as possible. I think my first question to the community was "can I use PL cement to laminate the transom, instead of epoxy?" Guess how that went.
Anyway, maybe try to build an 18 standard by the book first? Then a bigger skiff from aluminum? We had a big aluminum center console push around here (new england), maybe 20 years ago? Names like black lab/pacific, etc so I still see them around. Lots of happy folks.