Planned length? Sounds bigger than an encounter but more "adventure" length or hoping to go full campaign?
Reading the hook as "Launching an attack on the planet Gala along the Perlemian Trade Route, the Alliance fleet hopes to acquire territory and information by dispatching a specialized group of operatives to capture the Sith command center" has me thinking along militaristic characters although I had thought about someone who may be a "partner" for Gialle. Of course most of the character's I've done will require a bit of tuning to boost ability scores, reduce hitpoints, and figure out how I'd want to (ab)use Background with this last one being the thing that may mix things up most.