I'll answer some.
1. Yes, you'll make an account and it's very easy.
2. Don't know
3. I think the same for all the games. However you can add other accounts with Google play.
4. You can play as guest then connect with Google account or choose sign in with Google account and you will have a new team.
5. Yes. You can play the game: through the fb, Google, or just play as guest.
6. I think so.
7. You can create a Google account then it will head you to choose gamer id and profile.
8. You will choose through Google then choose your account. It's very easy
9. Yes!!! And the picture as well
10. Don't know.
11. I think so, you have the option to do that through settings tab. But why ? Connecting with one account is enough.
12. Yes. On any android device.
13. Yes.
14. Don't know.
15. Not many old players know that.