You can make a fbx in blender and rig an image. Then they will function just like normal models but be flat. From there you can use attachments for a helmet. Turn attachments on or off with blueprint script to simulate an equpping mechanic.
Quick Example: https://www.youtube.com/watch?v=UDNltehY70k
Slower Rig Tutorial- https://www.youtube.com/watch?v=6EmqDNp4Tfw
Helmet Attachments- https://www.youtube.com/watch?v=fJf5AOKJJsk
Inventory -https://www.youtube.com/watch?v=2Ot5udsHFVw
If you want to go pure paper 2D, I think the only way to do equipment is with image overallys via flipbook.
If you don’t mind a fusion:
You can combine flipbooks and rigged 2D to create all the effects you seem to describe in your post.
A random example:
Have the body and legs be sprite components but have the arms and head be to seperate mesh components. Rig the mesh components and add attachements as needed.