I decided rather than be any kind of smart, I wanted to go full starship troopers and throw as many expendable rifleman at my problems as possible. Turns out this works surprisingly well, and the parts I used to build this style synergized well.

The core concept: I'll not waste your time. Here's the big thing that makes this viable: Reinforcements and teleporters. When a marine dies, a teleporter creates a replacement of it and sends it to fight where that marine died. Reinforcement speeds up the respawn timer and drops a marine off near the fighting. The new marine is dropped off long before the teleported marine expires.

In short, what this means is: teleporter creates marine. Helicopter drops off marine. You now have two marines fighting, and at no lost ground. That's the bread and butter. Everything else is to support this concept. Your assaults will be slogs, you'll take many casualties (probably don't do this on planetary campaign), but by sheer force of numbers you'll overrun the aliens (a bit ironic, since you're supposed to be the small group of highly trained marines vs the overwhelming aliens).

What synergizes well with this: Engineering, to make the process of moving teleporters close to the front easy. 20 Ammo, So you can make longer and more sustained assaults, or start them off by dropping off even more marines with the reinforcement ability. In the late game when you have more marines more teleporters are needed to double your forces. Robotics, so that bases defend themselves against waves, freeing up manpower for your attacks. Minefields, robotics, and engineering go great since you can place minefields in assaulting waves dynamically and the mini-turrets easily clean up what's left.

In a fight, ammo tends to regenerate faster than its used to reinforce, so you can use cluster bombs or reinforcements to make your attacks more effective.

Oh, and don't get life support. You want your men to die.