Now I got a question... what does a Buckler do in 5e? As 5e only has shield, and not tower shield small shield, etc. The only ones I can find are homebrew for Buckler.

And... can you cast spells with a shield if you're not proficient with it? It takes only one open hand, unless you're a class who can use their weapon as a focus. The rules state you can't for wearing armor... and shields are apparently treated with the same rules.