It's easy to conceive of these plucky rebels having been thrown together by command in recognition of their admirable/unconventional/ruthless modus operandi, but how would you do it?

I would like to have maybe an intel guy and a bodyguard following a smuggler on some journey to transfer supplies from his ship. While this is supposed to be a virtual milk-run, the corvette in space gets attacked by a Star Destroyer and forced to flee mid-battle, stranding a squadron of Z-95 Headhunters who flee to the planet pursued by TIE fighters, engaging in the airspace above the stranded trio. The fighters engage in a long dogfight, with the Z-95s clearly outmatching the TIEs but slowly losing in attrition as the TIEs continuous reinforcements afford them the luxury of numbers. Finally there is only one Z-95 left but its systems are failing from sustained damage and it crashes into the forest ahead of the trio. Its pilot manages to crash safely with her astromech droid and from there she has to choose whether to head out or stay with her ship. The group meanwhile can choose to either attempt to investigate her crash site, which is several clicks from where the smuggler hid the supplies, or continue with their mission and hope the smuggler is willing to risk his ship to help the rebels. Whatever the players choose to do, the star destroyer starts sending waves of TIEs to hunt down the downed pilot and any rebels on the surface...

So way back in the day there was actually a published campaign setting where the PCs were all part of the crew of a small capital ship. The PCs actually each controlled 3 or 4 characters at once. They would each be in control of a member of the command crew, a member of ground teams, and a member of the crew and depending on what the action called for, each of the PCs played different characters depending on who was present at the location.

So way back in the day there was actually a published campaign setting where the PCs were all part of the crew of a small capital ship. The PCs actually each controlled 3 or 4 characters at once. They would each be in control of a member of the command crew, a member of ground teams, and a member of the crew and depending on what the action called for, each of the PCs played different characters depending on who was present at the location.

That sounds like the DarkStryder campaign from WEG

I am planing on a simple approach, all of the PCs have joined the Alliance and have been assigned to SpecOps, where they meet for the first time and get assigned their first mission together.