So to jump in.. The knowledge costs on Turrets are fine and may need a bump up. Especially if you have a Super Terminal.
In general, I ramp up AI progress to the 250-350 point, unlocking mostly turrets, forts, harvesters and fleet ships. I'm kinda an anti-Diazo, rather than minimizing my AIP, I maximize my defenses.
I set up the Starships, 1/3 of my forts, my Mark 1 turrets and a good chunk of my fleet on my whipping boy.
Everything else is set up on the ST World - 4+ Forts, Mark 2 and 3 turrets etc. Wait for CPA. Post CPA, run Super Terminal for 2-4 hours. Kill Superterminal at next CPA announcement.
Conquer remainder of galaxy at 300 AIP - minimum threshold.
When you have better technology than the AI, winning is fairly straightforward. Now, this DOES NOT WORK at 9.X difficulty.