Thank you for sharing more detail about your experiences with 3D printing. I’ll be interested in hearing how the 25% infill holds up, particularly in terms of parts like the Arm Bottom, Arm Top, Forearm Top and Shoulder.
I’m afraid that I don’t have any experience sourcing mechanical parts like the Torsion Spring. You should be able to figure out the approximate dimensions of the spring that you will need by examining the inserts for the spring inside the Shoulder and on the outside of the Arm Bottom. Have you had any luck finding a supplier?
Wishing you all the best in your assembly work and getting your robot working.