Major question: Yeah, you basically have it figured out. You only evolve when you both go up a level AND hit the main complex (Materials, Factory, Research, Access).
Minor 1: You can't use the God Mode code yet. You'll be able to use it when Warlord's branch is implemented though, sometime in the next version or two. The Recycling code is permanent, unlike most other codes you come by, so you can use it in future runs.
Minor 2: Good question.
While we're here, I have a question of my own. It's really dumb, but... Corruption refreshes back to 0% every time you level up, yes? I am 99% sure this is how it works, but it's not in the manual lol. I dunno, maybe it deserves a line in there somewhere.