So, I've never played Advanced Wars, but after watching some gameplay footage, I can say that you make a good point lol.
And you are correct, the character designs are based off Polandball (or Countryballs), digital comics made by people all over the internet. There are also many YouTube channels that use them. If I had more time, I would've liked to lean further into that art direction but 72 hours simply wasn't long enough.
Annoyingly everything you suggested was on my to-do list but I just didn't get chance to implement them :(
Sadly the music is only 30 seconds long, and half of that is the intro. My musician is more of a quality over quantity guy.