My thoughts re:fighters:
I consider there to be three real roles that a fighter can fill: Missile fighters, beam frontliners, and anti-missile interceptors.
Interceptors are still in the theoretical stage (Yes, still, I've been playing other games recently) and are all about maximizing speed at the cost of, well, everything else. Using the 0.6HS GC, you should be able to get the interceptor in under 150tons in the early/mid game transition, and down around/below 110 towards the end. Yes, it's true that, if you're dealing with missiles that are faster than the interceptors, they will be nothing more than glorified PD platforms that are less effective than their fleet based counterparts, but, when their speed matches that of the missiles, they excel in dealing with the over-saturation missile strategy that counters fleet based PD. This is pretty much the only potential design for an interceptor, as anything else will weigh too much to obtain the necessary speed. Hell, you're pushing the size "limit" just with the extra 0.1HS on the 0.6HS GC.
Frontliners are what you'd typically imagine for beam fighters. Mesons are fantastic here as they do a fixed amount of damage, whereas all other weapons benefit significantly from increased weapon size (15cm is about the size limit for fighters). However, if you're using beam fighters in conjunction with missiles, there's really no reason to use mesons as your opponent's armor will already be damaged significantly. *However* one thing I will strongly recommend is that frontliners should either have several layers of armor, or, even better, one or two shield modules. This is one of the few areas where I'd recommend shields over armor (Save for all but the very early game, but at that point fighters are already out of the question due to tech requirements) for two reasons: I'm under the impression that fighters cannot have their armor repaired, so if a fighter takes a few hits but survives, it will forever be a cripple, and fighters have an incredibly small armor width (Most fighters will be four or smaller, iirc), so there's a fairly high chance for internal damage to occur after only a couple AMM/PD hits to armor. A full sized ship could survive such a leak, but any internal damage will likely result in the fighter goin' boom.
As far as strategy goes for the frontliners, I'm inclined to just let'em float outside their carrier and act as additional PD until my fleet takes fire from enemy beam weapons. At that point, it shouldn't take long for'em to close the last remaining gap and quickly shred the enemy fleet.
I can't really give much advice on missile fighters as my current game is beam only (Well, and sensor buoys), but they come off as being a bit more flexible depending on the role you want them to fill.
Oh, one thing that should be mentioned, if you're aiming to use fighters to "turret" weapons that otherwise wouldn't fit in one, about the only weapon I'd consider doing that for is the rail gun during the early/mid game when the RG has an RoF advantage over the GC. I don't consider carronades to be viable outside of the early game, so those are out (A 15cm carronade is only remotely useful until you've acquired 15cm lasers). Particle beams are tempting due to their "constant" range, but you get more bang for your HS buck out of the larger variants. Fighters do, however, have an easier time obtaining a speed advantage for sniping ships. However, to keep up the internal debate, you'll be needing a 4HS BFC in order to take advantage of the range, which puts you well over the size limit if you want to maintain decent speeds (Hell, I'm thinking you'd be lucky to fit the smallest particle cannon on *any* fighter, let alone a viable one). I'm sure microwaves could be used effectively on fighters, but I've yet to come up with such a strategy (I was originally going for a microwave + meson mix, but decided to go pure mesons).
On the neutronium note, I was forced to hold off on expanding/building more shipyards early on for the same reason. Fortunately my shortage was taken care of once I established my first manned mining colony outside Sol that has several million at 0.5 accessibility. Not perfect, sure, but it's more than enough to take care of all the neutronium I can use when you take into account my current duranium production.
