Okay, so I decided to try it out myself, with as close to a beginner team as I could get. I was able to three-star it fairly easily.
I barely used any skills: I used an instakill skill on a 5 hp unit, and only Amber's special skill(heal all your units).
Some pointers:
- You get the two uncaptured cities to the right of you asap (should be turn 2 with the motorcycles)
- Then, you wait. Don't move your units, keep them near your factory, and try to kill the enemy units as they trickle in.
- Get some anti-airs early, your copter vs 2 of theirs is never gonna win.
- Always let damaged units heal in a city, unless they can kill one of the enemies.
- Try and have your damage spread out over multiple units, so your special skill can heal them all.
- Don't hurry, and spam light tanks.
Good luck man! And remember, the artillery is pretty much useless in the beginning, you can just pretend it doesn't exist