Yeah, sure, why not, mecha are always good. Stepping away from the standard real robot "gundams with a lot of guns" approach to a mecha RP is even better. Some commentary on the things that aren't set in stone and whatnot:

-For factions, I suggest having all the players be part of the same group, while inter-PC conflict can be fun I find that having to keep track of and managing two groups each with their own plots, stories, etc can complicate matters for the GM and players alike. Which group, I dunno. Maybe hold a player vote?

-For the tone, yes, a more super robot-style roleplay is good, because if you look around basically every mecha RP seems to stick to what can be more or less defined as "the real robot genre" something fierce, and while that's all well and good, having some a different style to the mecha would be real nice for a change.

-If by "revolutionaries" you mean the people who can manipulate elements, I'd suggest leaving that up to player choice, with the caveat that if someone chooses to not be one, they should not be screwed over because of it. Something like having to specifically construct Navirezes to channel the abilities which means they sacrifice other functionality (armor, physical power, mobility, you get the drill) for it. A fairly typical squishy sorcerer vs brawny fighting man divide for balance purposes. I'm sure other people can come up with other ways to balance this.

-As for characters, I'd lean towards original characters only. I'm sure someone'll be offended by this, but from my experience people tend to be bad at accurately portraying existing and well-defined characters in a convincing manner, and then there's the whole bit with fucking with historic characters which may or may not eventually become important plot-wise. sides a story about the unknown heroes and soldies behind the curtains of history has a nice ring to it, doesn't it?