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Gunship 2

I'm not sure this ship meshes with your stated tactics.

For starters, it is anything but lightly armoured - about 25% of its wet mass is armour, that's 1.5-2.0x stock Gunship's armour mass fraction and Gunship is already a ship strongly oriented towards close-in gun battle.

My own similar vessels have about 0.5x Gunship's armour mas fraction, despite being built for direct combat.

In any case IMO it would be a good idea to optimize at least some guns for defeating missiles and drones - you can finish a crippled ship with primarily anti-missile CIWS just as well.

However, I think you are right that aluminium radiator is too easy to melt, I'll create a new light-weight radiator for that.

The tactic/strat/doctrine I used when playing CDE is avoid gun battle at all cost, intercept missiles/drones mid-flight, use missiles/drones to destroy enemy, escape if mission failed, use flares and guns as last resort. In fact, with common sense plus this doctrine, guns aren't really that necessary. It would be more effective to be construct a laser-only fleet guarding few and large but highly maneuverable high delta-v missile/drone carrier.
But guns were added just in case of:
a). Missiles are precious, using guns to finish enemies off can conserve ammo reserve. Remember in WW2 subs often use deck guns to finish off convoys after escorts were destroyed?
b). If entire enemy fleet decided to force a gun fight by burning straight at us. Then the lightly-armored missile/drone carrier fleet will stand little chance against them, so guns and armors were needed after all.

1. I agree with the mini NTR might be impractical. Would love to build some alternative to that.
2. For this point, I would argue modern guided destroyers even aircraft carrier alone are pretty much helpless against swarm of missiles and piles of conventional guns (assume the ship is in range of them). But the over all effectiveness of a weapon must be evaluated base on the strategies and tactics it is designed to employ with. If one uses the modern weapon with World War 1 doctrines (recall Iraq-Iran war), then of course it never satisfies the need because they are used beyond spec.

Ok, two points:

1. Main reason why your Candles are quite scary is that they are effectively KKVs on top of being nukes. They can expend their (considerable) dv budget quickly, at which point, even when shot down they are capable of taking out a warship simply by impacting it. They are also manoeuvrable and seem to be able to follow through hull breaches created by others and explode inside. Good thing there are decoys and counter-intercepts. I'm still unsure if NTRs on misiles would be practical IRL, mind you.

2. Your ship seems pretty helpless against missiles and conventional guns. It doesn't have much in the way of PD, aluminium radiators are also easily flashed off by nukes and streams of heavy bullets can collectively cut through the armour.

I honestly do not know why is there a seoncd Gunship 2...

About the starving part, I would like to have some power reserves in the first place.
Secondly, I had tried utilizing maximum power, but power hungry guns simply takes all the power to charge for themselves before less power hungry guns were able to fire. (Especially when using lasers, I wanted to have 3x130MW lasers, but they eneded up starving all other guns and made them not firing at all)
This created a awkward situation where power hungry guns spending long time to charge while high ROF smaller guns had to go silence and wait.
This ultimately reduces fire power outputs and I decided it is not worth it.
If I ever need extra guns (or missiles), I prefer to add another ship instead.

In this case the idea is more or less the same.
If they want build spaceships, they won't build a single 100kt behemoth.
One lucky shot will be enough to lose the battle.
Also the armor and guns are for final phase of combat.
When delta V is really low or somehow the fleet is caught in gun range, then the armor will become revelant. Before that, the fleet should use missiles or drones (if available) as much as possible. (Or when all enemy ships are disabled and need to use guns to finish them off)

Imagine USS Ford going gun battle with PLAN destroyer Type 54, no missiles.
No matter who win, final result is not gonna look good and people back home will complain: why not use planes/missiles!

I agree, but given the complexity of the ship already, I would say this is good enough and any other capabilities should be delegated to other ships.
In fact, in the unmanned derivative of this gunship I actually got rid of lasers entirely (while reducing mass down to 9kt); there will be a separated, dedicated and cheaper laser ship variant to provide laser fire power (planned to carry 2x130MW laser, 80cm aperture, 10 times more powerful than stock; with 8 high accuracy guns for defence).
My thought used modern Aircraft Carrier combat group as reference. Militaries don't stack all the missiles on aircraft carrier alone. They produce bunch of cheapter destroyers and stack hundreds of missiles on them.

My own strategy with crew radiators is to use small, refractory material ones and place as many as possible without bloating the maintenance requirements. Like you said, they're tiny screws compared to the rest of dry mass, so sprinkling them liberally is not that much of a mass penalty.

Personally, I avoid placing CM's far from center of gravity - this allows hard manoeuvring and surviving all kinds of things that can knock ship around - nukes, flak impacts, ammo explosions, propellant tanks rupturing, etc. I do place reactors in more than one location, though, as they handle high G better.