I'm all for this, and I would be happy to play the fighter or the ground commander for either the Rebels or the Imperials. I have quite a bit of X-Wing stuff for both of those factions, and I plan on acquiring more Legion forces for both sides. I do like the idea of "buying" S&V starfighters for those engagements. I don't have anything for Armada and probably won't pick that game up anytime soon, especially now that Legion is on the market.
I was just throwing out the Rebellion board game as an idea; I think we could probably do this campaign without it. But we'd have to figure out how to track the campaign, and what we are fighting for. In the Halo campaign that Quickdraw and I just started, we are fighting over control of a specific system. Whoever controls the majority of the Forerunner sites on each planet controls that planet; whoever controls the majority of the planets in the system controls the system, and thereby wins the campaign.
My mind automatically goes to that model for a campaign (fighting for territory), but there are other ways to do it, other objectives to achieve. I'm more in favor of a campaign that is going on at the same time as the events from the original trilogy, not necessarily taking place in the same location (so no need to make a trench run at the end or anything like that). Star Wars is a big universe (no pun intended), so there could always be Rebel-Imperial conflicts going on in other places, like we saw in Rogue One.
We could also solve the physical models issue by pooling our resources. Like I said, I've got quite a bit of stuff for X-Wing; if I'm not the "fighter commander", I can make up a list of all the stuff I've got so that whoever the fighter commander is can borrow my starfighters to fill in the roster for engagements. We could do the same thing for Legion and Armada.
March is almost over, and April is around the corner. Given that Legion was just released, maybe we could look at starting the campaign in a few months...maybe aim for the first weekend in July? That would give us time to write up the campaign (not an insignificant undertaking, as I've learned here recently), add to our forces (buying, building, and painting), and learn the games a little better (especially Legion, since it's brand-new). We could have a few building/painting days for Legion, get some practice games in for all three games, etc.