For the forearm I basically repeated the above steps.
Cut out your three (might need four) forearm sections in template form and test fit everything in paper. The forearm sections are just one strip, not two combined like the upper arm. When you're happy with your fit, cut the plastic parts out using your modified templates.
Cut the the strips out and assemble each part.
Trim and do another one.
Test fit as you go.
To connect the sections together I cut a long strip of scrap plastic about 1 inch wide and riveted the sections to it.
Lastly, I cut two elbow sections out and riveted one to the upper arm and one to the lower arm. I cut out a circle and placed it over the elbow and rioted the elbow sections together in the center of the circle. the elbow pivots on this rivet.
The little squiggly line above the elbow is silver sharpie I was using to mark the plastic.
My circles suck because I free handed them. Use the template to cut nice circles.
Testing the size is most important here.
This might not be the best way to do this, so experiment and have fun.
I'll answer any questions but I won't be back online until this time tomorrow.