Okay, since all warnings of "Don't build it that big" are being ignored, might as well help with the turrets.
Here's how I design my large ship turrets.
Damage:
1) Backbone - Cannon/Cannon/Punchthrough and Cannon/Cannon/Stop
I call these my backbone because I consider them to be the main body of my defenses. Lots of Cannon/Cannon/Punchthrough, and I mean lots of them. So that a single opposing ship never has less than 3-4 of these that can target it at any given time. The idea here is basically a DOT (Damage Over Time), a steady stream of fire that constantly whittles the opponent away. Big super damage missiles are nice, but the reload on them is generally long enough that I get more overall damage out of my cannon turrets than anything else.
I usually do a single Cannon/Cannon/Stop (with Stop at 100%) down the middle, and 4 Cannon/Cannon/Punchthrough surrounding it in each turret. The AI has a lot of trouble aiming two different types of weapon, but these are identical except for the tertiary so there's no problem. Helps the cannon slow things down and pin them to the sky so that the rest of the cannons can punch a corridor sized hole into the target.
2) Decoys - Missile/Cannon/Explosive
Missile spam is the name of this game. Its not great against small fast moving fighters (unless they're getting pinned by the stop cannon above), but that isn't their goal. Their primary goal is to absolutely fill the sky with missiles. I usually have 3-4 batteries per turret to give rapid fire coverage. The idea is to initially overwhelm point defense by having more missiles flying than they can handle, in order to give the bigger missiles (covered next) a much better chance of getting through. However, the steady stream does much the same as the Cannon/Cannon once its hitting the target, just a heavy constant stream of damage melting through the hull.
3) Big Guns - Missile/Beam/Explosive
I go with /Beam instead of /Pulse. Pulse makes bigger booms, but the missiles fly slower and take forever to reload. /Beam does less damage, but the missiles are lightning fast and much harder to shoot down. The trick I use on these though is that I have one massive missile as the primary damage, and then flank it with little baby 1/1 Missile/Beam outputs half a dozen blocks or so ahead of the main output. These serve as decoys as PDT tend to go for the nearest missile first, so that gives me two decoy missiles flying in formation just a few meters in front of the real one as a last ditch attempt to save the main payload.
Ratio wise, I try to use these at 4:2:1, aka for every big gun I have two decoys, and for every decoy I have two backbones. On top of that, I also like to have a defensive PDT close to each turret. Its a holdover from when turrets were exposed at 50% shields, but I still do it out of mostly overkill. If my shields are down, I don't want any missiles targeting my turrets.
Crippling:
1) Power - Beam/Cannon/EMP
In my experience, most ships (especially larger ones) do not have sufficient power generation. Oh sure they have lots of battery power, but often times they install only enough power generation to let them run all their stuff at the same time. That means they have a razor thin margin, and a good strong EMP weapon can easily tip the scale to where their shield regen/weapons/thrusters/etc work against them, draining their batteries faster than power gen can restore them. And once you can tank their power, the fight is basically over. No power means no more shields, no more weapons, they're just a big old sitting duck
2) Shields - Beam/Cannon/Ion
These are less about actually collapsing the enemy's shields and more about making sure they stay in constant regeneration status. Regenerating shields suck power like crazy, and as stated above your ship stops working when you're out of power. Don't get me wrong, they're great at collapsing shields too, but odds are you're going to get most of that you need from your offensive turrets, this is to me mostly to ensure a steady drain that they just can't stop.
Personally I merge the power and shield aspects into a single turret to make finding space for them easier. Lot like I do with the stop cannon, just with the EMP beam being the main gun and some secondary Ions for harassment.
Defense:
1) PDTs - Cannon/Cannon
Simple 1/1 Cannon/Cannon turrets set to Aim at Missiles. Some people like to add in some cannon/beam here and there for long range sniper shots, but in my experience the low hit rate means those are unlikely to actually hit the missile before they come into range of the cannon/cannon, and its all about throwing as many shells into the sky as you can. Pure spray and pray seems to be the most effective anti-missile tactic for me.
In fact, I usually have so many PDTs that I've actually designed a low profile turret (only stands 1 block high above the hull) that looks like a giant rivet so that I can just put them EVERYWHERE without making the ship look bad. Did I make a big armor plate looking structure somewhere? PDT rivets in every corner to look like they're holding the thing in place while also giving crazy amounts of point defense.
2) Anti Boarding - Fixed Cannon/Cannon
If you're building a titan, odds are you're going to get boarded at some point. A fixed turret (a turret on a single axis that has the barrel locked in place so it can't move) still has a 30 degree field of fire, which makes it ideal for shooting down corridors/hallways. If you've got any long straight hallways, put a fixed cannon/cannon at each end powerful enough to one shot an astronaut. Don't go all RP friendly "let them figure out its there and have a fair chance to get around it", just freaking vaporize them on the spot. You could use beam/cannon for a more solid lock, but that just paints an obvious line right back to the turret. Cannons make it harder to follow them back to the source for any secondary players who are watching that first one's head explode.
Some people like to have pulse turrets hidden behind the walls for this, but especially when crews come out I don't want them hit by friendly fire (as much).
Pro Tips:
1) 1:1 Ratio Output/Computer
Never have more than one output linked to a single computer. You get a power tax of 10% for every additional output a computer controls, and the AI can fire all of it's computers at once (unlike us humans that have to fire one at a time). If your turret has 4 outputs, it needs 4 sets of computers. You save a TON of power that way.
2) One type of weapon per turret
Each turret must be only cannons, beams, or missiles. Never mix and match. And never mix/match missile types on a single turret either. Reason being that the AI is, in a word, stupid. A cannon shot takes a few seconds to reach the target, a beam is instant. If you have both on one turret, the AI won't be able to switch the aim back and forth between shots. It will either lead the target for the cannons, and make the beams miss, aim at the target directly for the beams and make the cannons miss, or more often than not shoot somewhere in between and make them both miss. Same goes for the missiles, different missile types have different missile speeds, if you have dumbfire missiles with different speeds on the same turret, the AI will miss more often than not.
3) Self Power Smaller Turrets
I mentioned above about the fight being over when your power is gone and your weapons stop firing. Thats not entirely true for turrets. If your turret generates enough power to cover it's own firing needs, it can keep running even when the main ship is dead. Power gets pulled up from the main ship to the turrets, not the other way around. If the turret can power itself, it can keep firing without pulling from the main ship, which means it can't be indirectly shut down by the main ship losing power. It makes the turret bulkier, but a good build can hide that power generation in the turret base that recesses into the hull of the mother ship if need be to hide it.
Thats going to be impractical for big guns, but the cannons and maybe the missile/cannon turrets will likely be small enough (power requirement wise) to run themselves.