I love the concept and thought put into these suggestions, wonderful job!
However, I envisioned metalbending, relative to earthbending, not only using personal sources such as iron acquired in their inventory or armor, but also from surrounding sources. While the metalbending shields are amazing, and well thought out the way they are now, I would like to see not only uses for direct combat, but also defense of a potential metal city. Similar to how earth can extract sources from the ground, possibly metalbenders could use source blocks such as weighted iron pressure plates, iron doors, iron blocks, and possibly iron related blocks such as the iron trap door featured in Minecraft 1.8.
These metalbenders are drawing their sources directly from their environment, so I would love to see this being a possibility for most of these concepts.
I hope you like the suggestion, and feedback is always welcomed, thank you!