I'm just getting my fleet started but you may find my doctrine useful so here it is:
Currently I'm at going beam-only but will eventually design missile ships. My shipyards can handle up to 19,200 tons which I'm designating as "Light Cruisers". CLs all share the same size, engines, speed, and shields. Each fleet will consist of the following:
One Command cruiser: Jump drive, flag bridge, one of each size 4.5 sensor (EM, Thermal, Res1, Res 6, Res 20, res 120). 4K tons of Hangar deck space.
This ship is the jump tender, command/control ship, and homebase for my scout fighters. The res1 sensor is for advanced warning of incoming missiles. 1 small cryo berth for picking up escape pods.
8x 500t scout fighters, 2 each with size 4.5 sensors (Thermal, Res6, Res20, Res120). Res 6 detects fighters, Res 20 for FACs, and res 120 for large ships. The fighters move at 5200 where the fleet moves at 4000. They are expendable sensor platforms - fairly cheap to replace and they don't give away the fleet's location if detected.
Six Beam cruisers: each with a res1 sensor for targeting. With a mix of lasers for offense and gauss cannons for point defense/fighter swatting.
Once I start producing missiles I'll add
Three AMM ships: Size 4.5 res1 sensor, Size 1 fast reload launchers, and magazines
Six ASM ships: Size 5 20x slow reload launchers, magazines, one size 4.5 sensor either res 6, 20, or 120.
By making the magazine size the same between the two missile carriers I may be able to have one shipyard churn out both types.
2x collier - commercial magazines and ordinance transfer systems
2x tanker/tug/supply ship - refueling system, tractor beam, one shuttle bay, and a few large maintenance storage units
2x fighter transport - commercial hangars
Two of each so one can stay on station while the other heads home if additional resupply is needed.
If you have sufficient range and speed on your AMMs/Res1 sensors you can have time to launch multiple AMM volleys against each incoming salvo, which will let keep both leaks and wasted missiles to a minimum.
For salvo estimation - well, see how many missiles your AMM ships can handle and that's probably about how many the NPR can, assuming they are the same size as yours. From a practical point of view if you have the range advantage you could launch once then keep the range open and watch to see how successful it was, then tune subsequent volleys accordingly.
Note: I haven't fought a missile engagement yet in C#, so you'd likely be better off listening to advice from others on the thread who have experience in those things.