You probably have to many different sizes of launchers.  They are all going to have different cycle rates which will dilute your total weight of fire dramatically.  I would go with three sizes.  The size 1 launchers for point defense, the size 24 for really long range, versitility (sensor drones) and the ability to use multi warhead missiles against fighters and gunboats, and one other size that will be your primary anti ship size.  My suggestion would be to go with the size 12 launchers as they are large enough for lots of options, and they are still fairly fast firing.  

One thing you might want to try is a multi warhead missile.  Put a several very short range missile with a large warhead (size 2-3 total) and fairly fast for the final stage, and a large fuel and engine for the first stage.  If the first stage is twice as fast as the ships you are firing at it will have a long range, when the second stage fires they only last a million klicks or so, but that gets them through the point defense envelope pretty well, and the defense will probably have wasted their first few pd salvo's on the bus stage.  The bus stage is still going to continue on and so it will absorb their counter fire as well.  You can do the same sort of thing to engage fighters and gunboats as the second stage missile will have a much better to hit given it's higher base speed.  If you do want to go after fighters though, you probably want to reduce the warhead to 2-3 points of damage, and up the agility as this will work better.

Brian