Once again from the foggy recesses of my mind...
I have typed some of it before here so it may be familiar to some and a search might turn it up though it might be a bit differently remembered
And of course I keep stealing ideas
but I think some of them are mine...
So, imtu the standard missiles (50kg) are really nothing more than a munition. A hyper-velocity smart munition but basically just a big bullet. There is very little in the way of thrusters (terminal aiming) and the turret launcher is what gives it the huge kick that sends it to the target so yes it needs to aimed. These are the civilian missiles and are conventional warheads.
Next up from these is a heavy missile (150kg) which is a paramilitary or military version of the above. It fits in the same volume as the normally 3 ready standard missiles per launcher. Being heavier the launcher is used just for a primer kick and then an onboard solid rocket takes over for a short boost phase. Again this all happens right at launch so the turret must be aimed. The larger payload allows a bigger warhead and advanced electronics which gives this missile the same punch as 3 standard missiles and the defender is required to make three successful defenses to stop it. The paramilitary version, available to accredited mercenary operations, is a conventional warhead. The military only version is also available in a nuclear warhead version. It is illegal for civilian ships to possess either of these. (see pg.245 ed.1 of T20 for a picture that to me shows a double missile launcher with two heavy missiles just fired).
Imtu missiles have the long range (as listed) but because of the high velocity they hit (if not stopped) at the end of the turn. I don't do vectors for missiles. By comparison the reason energy weapons take a full turn to hit is beacuase they are saturating a cone of probability with lots of shots. I worked it out a little bit ago for T20 and think I came up with a shot a minute based on converting to vehicle scale.
The only actual maneuvering missiles imtu are the full size bay weapon torpedos which are about 1ton each (450kg of payload and 450kg of thrusters). These are what I would describe as the guided or smart missile you are describing. The bay launcher is used for loading and popping these. I think I worked out 1 per turn (single tube) for 50ton bays (which hold 25 torpedoes) and two per turn (two tubes) for 100ton bays (which hold 50 torpedoes). These do not need to be aimed and maneuver to the target. They have advanced stealth and electronics and multiple warheads, conventional only for paramilitary with a nuclear option for military. I also use these for drop capsule launchers, replacing the warheads with the BD Trooper.
Something like that. I'm still ironing out the wrinkles and need to compile it all so I stop confusing old and new
since it's been in development for some 20 years (it's back to the drawing boards to check everytime they change the rules). Now with T20 it's about come full circle back to the basic CT ideas