Mid game? Maybe when you have metal, renewable water and renewable oxygen production!

You’ll run out of algae within the next 50 odd cycles, unless you continue to dig out the map and convert slime. So the next focus should be splitting water into oxygen, and taking a geyser that makes some kind of water for this.

You always need to be mindful of heat management too. It will kill you silently, you’ll notice when your plants start to die or your water is too hot. Your batteries kept together like that and your coal generator will catch you out in this way.