The main problem is I do not know how to analyze the 4 load points then arrive at a tubing dimension for hi strength aluminum.

Hi Gene,
If the four load points are the float, your heel, the near gunwale/deckline and the far gunwale/deckline, you can basically ignore the far side load point leaving a simple load calculation for a beam/tube supported at the ends and loaded at some point between.
A practical method to test the load limit of a paddle shaft is to support the shaft at one end and where it would rest on the near gunwale and do chin-ups. If it bends/breaks, it's too weak and you need a stronger tube.

We are curious how a 2x4 would paddle more effectively than a Camano.

A 2x4 would not paddle more effectively than a Camano, or any other paddle, even the terrible cheapie, two-piece paddle/shovel I have laying about somewhere.
However, a bit of wood removal from a 2x4 so that it forms a more refined shape than a plank of wood and it would make a nice paddle, a suprisingly versatile form of paddle. I can do chin-ups with my Greenland paddle.
Though not having used a Camano, I might find a 2x4 plank better.

Mike Savage
South West Cork