Having different tertiary effects on the missiles is a personal choice, not really germaine in my opinion to the question of salvo size and timing. I do agree big time however with varying the salvo such that the missile strikes are staggered.
I have just such a missile system defending my station, a station that regularly get visited by pirates, including at least once by a large fleet of much larger, enhanced, non-standard pirates. Going to examine the wrecks of the pirates afterwards was instructional. Each pirate had one or two tunnels that had been bored into it by successive detonations, clearly by missiles following one another and striking inside the hole made by the ones prior.
This effect is much easier to achieve on a station where one can be somewhat cavalier about letting the station run out of power. The trick is to have turrets on the station that are capable of firing 'more' missiles in a single salvo than the station has 'both' in power storage 'and' can generate in 45 seconds. What happens of course is that the station fires off as many as it's power stores can fire, then piece meal fires off the remaining missiles as it gets the power to do so. Of course the missile launchers are generating power as well. I set it up with ten such launchers, each having in excess of 100 missiles (15 missile/15 beam/5 ion) and generating a couple hundred thousand power each on their own. (Yes, these were not small turrets.) Each turret would keep up a steady stream of around two per second till everything was dead.
With ships it is a bit more difficult. You cannot afford to have more missiles than your power can handle, else you really will find yourself in a ship with zero power for anything else. The trick then is to vary the missile/beam ratio with a full lineup of missiles (EG: 20 missiles in a turret from 39 missile/1 beam to 20 missile/20 beam, plus a good many tiny missiles of similar ratios for point defense bait). Your first salvo will of course fire everything, but because they will have different speeds due to the different ratios of missile/beam, they will arrive staggered. This will have the downside of making them easier to kill with point defense. The trick there is to also have several tiny missiles with the same sized ratio of missile/beam whose main job is to soak fire so the bigger shots have a higher chance of piercing the active defenses. Once you've fired the main salvo, after fifteen seconds, you start tapping the fire button every second or so to fire off those faster cycling weapons that are ready to fire again. On a ship, especially if you are using turrets, be absolutely certain to have sufficient power storage to be able to fire everything in one shot without running out of power.
This approach is easiest when built into turrets so you don't have to worry about hitting the fire button. I should also mention that all combat experience I have had with this sort of thing is prior to the new HP/armor system. The effectiveness of this approach may well have changed.
