Ok, so:
1. That means capturing several additional planets (at least 3) to get L5 turrets OR spend half the research I've acquired this game on turrets OR both.
2. I don't know what they're going to attack with until it's way too late to build those turrets at runtime, so I would have to build them in advance.
3. Even then, that literally can defend 3 planets, because 30 turrets of each defensive type means I hit my cap. If I don't know where they're going to attack, how exactly does this setup help? I must be missing something major, here...
That screenshot just shows the optimal setup.. how the Turrets, Force Fields and Command Station should be positioned for maximum efficiency. Force Field(s) protect the Command Station.. Turrets protect the Command Station and the Force Field(s) Protecting the Command Station.. Tractor, Gravitational, Flak and Lightning Turrets protect the other Turrets.. Force Field(s) protect the Tractor, Gravitational, Flak and Lightning Turrets.. Counter Sniper and Missile Turrets protect everything. All of this should be built right between the Command Station and the hostile wormhole. That's because of the AI pathing. When AI ships come trough the Wormhole
(or spawn at the wormhole if it's a wave) they move in a straight line towards your Command Station. When you build a Force Field(s)
(and the other stuff too) on that line it will interfere with their movement.
I'm not saying you need to unlock all of those. That's just how it works. If your defenses
(if there are any) get overrun then you need to unlock more defensive stuff (Turrets, Force Fields, Minefields, Military Command Stations). You have to decide what you need and when. All of this depends on the map seed, AIs and other stuff.
You do need to know
(and control (gate raiding)) where the AIs are going to attack
(open the galaxy map and press W to see hostile wormholes) because that's where you're going to build your defenses. But you don't necessarily need to know when they attack. The purpose of defenses is to prevent
and stop attacks if and when they occur. If you don't have defenses.. then obviously there are no defenses to prevent or stop attacks.. so you need to be prepared. You
should not have undefended planets adjacent to AI planets. You
should have 1-4
"whipping boys" where you take all the waves
(whipping boy=a heavily defended planet where the AIs send their waves). I said 1-4 because that's the number that usually works. In most maps you
must have
more than 1 or 2 whipping boys because that's usually not enough to create a chokepoint. The AI will be able to go past the whipping boys. And 3-4 because that's the maximum number of whipping boys that will be able to stop waves and other attacks
(CPAs..). You can only have a certain number of whipping boys because you will run out of Turrets and other defensive stuff so the defenses wont be strong enough to stop the attacks if you have 37 whipping boys. Obviously if a planet doesn't
"take waves" it doesn't need as strong defenses. But even if a planet doesn't take waves it can still be hit by a CPA if the CPA fleet is able to past your whipping boys. That's why people build chokepoints. The purpose of whipping boys is to take the attacks and stop them.. and to protect the other planets.. and ultimately your Home Command Station.