(just my 2 cents, I realize I’m not answering your question exactly…)
Have you tried/considered using something like Blender?
In my mind, 3D design is a bit split between “technical stuff”, with measurements and precision and blueprints and etc, and “organic stuff”, like figurines, sculptures, etc, etc.
You can do both types of things with both types of software… But most will be easier in one or the other.
For example, if I’m 3d-printing something to hold stuff around a shelf, or clips to join things together, or something “generally functional”, i’d use CAD, but if i wanted to 3D print something nice-looking and non-functional, i’d use something in the Blender type of software.
An Iron-man armor kinda falls in between those two, since it need to be functional and have actual measurements matching your body… Plus you might want to have mechanisms around the face / arms / etc that could benefit from CAD.
But it’s also very “organic” and looks will probably matter more than precise parametric design… And more importantly in my mind, I expect there are hundreds of 3D models of iron-man you can take and adapt. These will be meshes, not parametric / STEP files, and you’ll have a much easier time, IMO, modifying a mesh of triangles in Blender than in CAD (again, both can do it… but CAD is not built around mesh manipulation as much).
If I were doing this myself (and I’ve thought about it many times 
), I would start with an existing mesh and start “skewing” things to fit my body, as opposed to start designing from scratch.
Again, just my 2p