If you're having trouble with excess ninja outposts, I've got them down to something like a science by now.
Certain craft are your friend for this, early game I'd recommend the CONVOY. Throw some HMG's or 25mm's in the gun slots and ensure the pilots are high-accuracy and it'll plow through enemy interceptors on the way in. It comes as two open backed APC's, so sometimes your landing zone can screw you. If you spawn in with the open doors facing the outpost and its attendant 14mm's just leave, it's not worth it. Once landed, your convoy is your fortress. Engage enemies by "poptarting" using the two ladder/hatches on each apc to pop out, take a couple shots then drop down. Use sniper rifles, grenades/grenade launchers and bows to eliminate the minigun turrets (the little ones) as well as any ninja you see. Ensure you're clearing the space around your APC and be careful about ninjas throwing grenades into your craft. It sucks.
Once you've cleared the flying assault ninjas and minigun turrets and have a little bit of breathing room, start pushing gals out into good cover to approach the 14mm turrets. Be careful of ninja in the little corner fortresses. For this next bit you need flamethrowers. Flame throwers always do a little bit of damage even through armor, hit AOE to take advantage of the turret's 2x2 profile, and reaction disrupt to keep you from taking return fire. Lucky for you, random ninja slaves tend to carry flamethrowers on these maps if you didn't have some already (you should have some already). Beat the turrets by hiding in the crenelated portions of the wall near them and popping out to hit them with burst from your flamethrowers before popping back in.
It is *possible* to damage 14mm turrets with your normal dedicated AT weapons (RPG's and such) but they're tanky enough that it will take multiple hits, and they absolutely will reaction fire and kill your shooter every time. However, if you hit them with a flamethrower first, they'll be disrupted and unable to fire back at anyone else you have shooting. Turns out being covered in burning napalm limits your ability to see very well. If you're especially bold, you can use this time to whack them with hammers.
Two dedicated gals with flamers can burn down a turret in two turns. Less if you supplement with RPG's, hammers etc. Once both turrets are gone, crack the main gate with a hammer and commence to hunting ninja's. By this point you should have killed enough of them that the rest are panicking and will surrender, but it is sometimes a chore to hunt down the last stubborn warrior.
Once that's done, enjoy the cash, loot and score bounty.
It's possible to do this very early on with very low resource investment. A couple high accuracy gals with snipers or grenade launchers form your base of fire. They sweep the skies and kill mini turrets. A pair of gals with flamers to push up and handle the big 14mm's. At least one gal with a hammer or pickaxe to break the gate. Convoy is optional and there are better craft for this (anything with a door and no windows, looking at you TRITON), but it's cheap, tanky and available early on.
