Presumably "outer" planets were those that bordered the AI and could receive waves, while "inner" planets would be your safer, interior, worlds away from the AI borders.
Ion Cannons, and Golems, and other things used to produce enhanced AI response once upon a time. I don't really remember it, because it went away in 5.0, so I played the tutorial (maybe not even all the way through) and pretty much nothing else before 5.0 and Light of the Spire came out. The linked Mantis entry gives a good representation of what I heard about it and why it went away.
What I remember... the good old days of Dyson Gatlings being able to produce unlimited sized hordes that would utterly crush any AI fleet...
Or the brief time period between 5.031 and 5.033 when Mk III Harvesters gave 73 resources/second...
Or the pre-hacking remodel, when it was possible to K-raid (using Science Lab Mk IIIs!) the galaxy with no real drawbacks...