I am so bad at the right angle studies, but they are also so interesting. I would like to get good at it, and can definitely see the merit in it. I mainly rely on images on the internet for most of these exercises (which is not ideal, but I am assuming it's better than not doing the exercises). There are some sites with 3D models/scans, which is fairly good for the right angle studies. For instance,
SketchFab (there are some free models, though I don't think there are many free human models) and
Bodies In Motion (3D scans of people, but require membership/payment). Nicolaides has also said it's good to do the right angle study with objects, which I need to get around to doing.
I don't think I really understood instructions for the watercolour modelled drawing. I ended up consulting the comments on
this blog post on how it works, and I think it seems to work a bit better towards the end. I initially tried to treat it like a watercolour painting, which is not the point of the exercise at all.