Hey there! Appreciate the kind words and the detailed questions.
1) That's an interesting idea. As far as we know there aren't plans to make that a feature, most likely due to servers and all that fun stuff. We do have those regions face off in our World Championships though!
2) So we hinted at it in our AMA video, and there is nothing concrete yet, but we are looking at possibly bringing back Classic Zombies to COD Mobile in the future.
3) Yeah, space is a major concern for the team as well. We are looking into adding some new features to optimize space and storage, although it's too early to talk about them now, but it is something always present on the team's mind. In the meantime, you can always check out the download manager to see if there is any content you can delete and play without.
4) Yes! We have some content coming up in the next couple of seasons that is pulled from classic COD titles.