pauldron rig approach

[EricTRocks]

You should listen to your friend for the most part. It's going to be a more complex setup if you want it to automatically collide with the rest of the body. It's not easy to explain this setup honestly and takes a good amount of rigging / simulation experience.

The cape should be done with a cloth simulation like Syflex or maybe the Verlet Integration using ICE. With Syflex you can use pins to stick the top to the closest meshes.