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Since 2300AD's release, I have run four campaigns set on Aurore, for as many as nine, to as few as two players. Aurore is still my favorite long-term location for running military campaigns ( for one shot adventures with novice 2300AD players, it is instead Mission Arcturus).
1) Nine players as an 8-man USMC squad, with an attached French liaison noncommissioned officer. I sent them through Mission Arcturus, and then on to Aurore. They were part of an Amercian Marine advance platoon sent to Aurore to learn about fighting the Kafer first hand ( their overall goal was that what they learned would be incorporated into USMC training/doctrine). They operated out of the French colony. Each of the three squads operated as a long-range patrol/raiding force, and as attachments to larger French units ( usually company sized). They are kind of a combination of the WW2 Marine Raiders and a modern ( 1990's) Marine Force Recon.
This squad also had a friendly competition with another squad in their platoon over who bagged the most Kafer/pulled off the biggest success. It made the world seem "real" to hear the NPC squad bragging about their successes, or moaning their travails.
2) Four players ( three were from the first campaign) as a USMC fireteam detached to the Tanstaafl colony. Their mission was part observation ( learn how the Ramrod Teams operated by going out on patrol with them), and part instruction ( they formed a small training cadre instructing in tactics and donated/loaned American weapons). They also interacted with the rural civilians, providing instruction in improving defenses of the various farmsteads/mines. This provided a mix of front line missions, civic action, and adventures in the rear areas ( bar fights, taunting REMFs, liberating supplies, chasing local women, etc.).
3) Two to three players as a USMC tank section operating out of a base in the Tanstaafl countryside. The PCs were the crew of one tank, but when out on patrol, the players running the driver and gunner besides running their own characters, were given "control" of the other two NPC-run tanks. Since mainly the PC gunner player made the to-hit rolls for their tank, I let other two players roll to-hit for the NPC tanks.
4) Three players unjustly sentenced to a French Foreign Legion penal battalion, triggered by their actions up to then in a Law Enforcement/Investigation campaign. They mainly spent their time avoiding the sadistic FFL guards, and trying to escape ( which necessitated removing explosive neck collars), while doing every dangerous job the French did not want to give real troops. They were considered very expendable. You could do a variant of this as a "Dirty Dozen"-film type of team assembled by the Americans ( or any nation on Aurore), without the collars.
It also avoids the "ho hum, what is this our sixteenth group of Kafers we have surprised tonight and decimated" player blues/boredom.
The Aurore Sourcebook has all of those wonderful chapters on flora, fauna, terrain and weather. Use them to the hilt, give the PCs something other than just Kafer to worry about. When the planet has them flustered/frustrated, then add Mr. Kafer as a further complication.
Sometimes the world will make it "easier" for the PCs, so do not forget to show Mr. Kafer having trouble with the planet too ( a mixed blessing since a frustrated/angry Kafer is a *smart* Kafer).
A squad sized or smaller units of PCs work best for the following missions: patrol, search and rescue, outpost, long-range recon, sniping, intelligence ( snatch equipment/personnel/?), survival ( stranded by failure/destruction of vehicle, and now must make it back to friendly lines), civic action ( construction, medical), to name a few.
Just beware of falling into the habit of *always* throwing too big a Kafer force at them, and then having the "cavalry" come over the hill to save them.
On the other hand, once the campaign is established, and people have created personalities for their characters, using a relatively huge "unstoppable" Kafer force once ( at most twice) has created some of the most tense and unforgettable role-playing in my 2300AD game sessions. Two players' PCs made the choice "in character" to risk the ultimate sacrifice ( death) of their PC to save the others. One PC died heroically, the other was wounded severely but evacuated safely. The Marine camp was renamed after the PC who died, also both received medals -- and all the players felt the two PCs really earned them. A third PC, "in character" with the PC's established personality, turned coward, and tried to pull a "Carter Burke" ( ala the movie Aliens) and he got what he deserved when he blew two critical observation rolls in a row.
Note: Beware vehicle campaigns, one hit can take out the entire PC group if they are all riding in the same military vehicle. So fudge the results, as you do not want to spend 80% plus of your gaming time continually rolling up replacement characters. Cripple the vehicle, or convert the damage into a noncatastrophic hit location ( say a crew or mobility hit). They will have more fun roleplaying getting out of their new trouble, than having their PCs killed off by the "magic bullet" ( a random catastrophic hit).
If you want bigger battles/fights, then attach them to a larger unit. Now describe ( play out) the battle from their point of view. They see just their portion and hear about the rest over their communication/data links ( or after it is all over back in the barracks/bivouac).