Interest Check - Gundam Style Mecha
Hm. One possibility would be to split the players into two groups: one Earth and one Space. Then you could tell the stories of each faction. They're probably both thinking they're innocent and in the right, and perhaps there's more than just one way to complete the story arc of the war. Not to mention the tales of friendships and rivalries across enemy lines to be told. The problems there would be a) few people dig the PvP that would create (it's like running a Smallville game), and b) slowdown on one side would make for some lopsided play. Maybe not a good idea. Hm. Well, my vote is for whichever side is the least evil and most outmanned and outgunned. Because I'm like that.
I have a couple of the supplements, but doubt they'll be useful to this game. You're really better off just looking at the Steel Gunner setting in the book and tweaking that to suit your needs. Sounds like you'd just need to take out the psychic demons, set one of the factions in space instead of another continent, and you're good to go there.
Personally, I'd just suggest removing Skills and instead setting a standard difficulty of 3 or 4, but that's because out of the six skills, only Mecha Combat is likely to see more than one use per Episode, and whoever has that even one point higher than the next guy is at a ridiculous advantage. (By that same token, I'd suggest rolling a new Initiative order each round, otherwise whoever specialized in that is going to be so sad.) Other than that, the core book has all the rules you'd need for a Gundamy game. I've been itching to try out this Combiners book, but this is not the setting for that. :P