> (3) How do you figure the angle to cut the sheer clamps at stem and stern?

The simplest way to cut shear clamps so the ends have a perfect fit is as follows:

First cut them approximately to the right angle, but leave plenty of extra wood.

Hold them together with a spring clamp (perhaps a rather weak one) or whatever else works in their proper position.

Saw through the joint with a handsaw (you will need to have the spring clamp at an angle that is out of the way). Be careful to keep the saw perfectly vertical.

Repeat the sawing until the joint is fitting how you want it. It may take 6 times or 16 times, depending on how much excess wood you initially left, but the two sides will be a perfect match, and the slightly rough saw cut will bond to the epoxy much better than a smoothly planed surface.