Evacuation is possible as long as your troop ships have cargo shuttles but it'll take a while. Usually you have to sacrifice part of your force as a delay action.
Using drop-pod-stations is an incredibly novel idea. I've never heard of anyone doing something like that. The downside is that if your tugs are ever busy when you need troops, you'll be in trouble.
Double check what stance you've set your brigades. If they are set to Rear or Support, they will only use artillery. Either Frontline Defence or Frontline Attack will start the battle. Infantry and Static should use FDef to maintain fortification bonus while vehicles should use FAtt to gain evasion bonus. But since the enemy has an incredible tech advantage, I would recommend Dunkirk-in-Space and further orbital bombardment. You'll lose the xenoarcheology loot but can start a mining colony afterwards. Alternatively, now that their STO is gone, you can just leave them and come back in a century with ultra-heavies of your own.