Do you guys think it's more important to star up as many characters as possible for the platoon missions or work on the top LS/rebel characters to have 3-4 solid G10+ teams for combat missions?
Yeah, agreed. Assuming you're not in a top guild, not being able to fill out the platoons makes it harder on everyone else who is battling. So, for guild effort, if you're trying to help, simply starring toons will do the most good.
For good Measure you can also level them to 30-50 pretty cheaply to get some more GP.