The New Summons System

[Fynn]

1. No, that's NOT Maqui. He looks completely different (for starters, Maqui has goggles). He is not a member of team NORA and seems to be a major character, so chances are he's a member of the main party.
2. Yes, that's Gadot, but this has nothing to do with the kid. He's from team NORA, and as far as we know, they're temporary characters (hopefully).
3. Yes, we're talking about the same trailer here.

EDIT!

Here are two articles from FFWiki. This is an article about Maqui, along with pictures, while here is an article about l'Cie where it clearly says that the kid (seen on the screen) is an l'Cie and is stil unnamed (which confirms he is not Maqui)...