Wow long thread so I'm here focusing on the first topics, some points I don't think were addressed yet (if they were plz forgive me).
Oh my you like efficiency. . . I can relate. But that's the reason why I tend to prefer beams. Well, when I use missiles, which is not often, I tend to use my extremely efficient design: a first-stage manned missile (aka fighter or FAC), which needs no sensors, just a simple fire control and a cheap engine, can change targets as needed, can evade incoming missiles (and even shoot them down if escorted) and you can reuse it later!
Or as mentioned by others, a small corvette or frigate with a single fire control, a few missile launchers and a small magazine.
Seriously, sensors on a missile, except for very specialized designs, look like a waste for me. I send my missile ships with a specialist sensor scout (and a few PD fighters for antimissile defense), so I need very few sensors overall, and they can be bigger. My range for antiship missile combat is between 30m-50m km max. Well, I tend to play with low/slow tech, I don't know how much it changes at higher tech levels.
A few notes on missiles:
1. your sensor on the 1st stage may be able to switch (randomly) to another target if the first is destroyed, but AFAIK you'll also need sensors on *every* second stage missile, because the 1st stage can't guide them;
2. your 1st stage need not have *any* space allocated for agility, it's completely useless unless you actually intend to hit something with it. It doesn't affect survival rate against AMMs or PD;
3. the larger your missile, the farther away it'll be detected;
4. on a two-stage missile, a slow 1st stage with a shorter separation distance will probably be a sitting duck for the antimissile missiles (AMMs) your enemy will surely fire at them as soon as they're detected.
A last note: taking advantage of the last point, I'll try a new design in my current game, which is a two-stage missile, whose 1st stage is exactly twice as fast as my attack fleet. The second stage, with 3 sz1 missiles, is as fast an antiship missile as I can make it, with minimal warhead and no agility, and the separation distance is at least 50% greater than the distance I estimate the 1st stage would be intercepted by the enemy AAMs. No sensors in either of them. There'd be volleys every 5 secs. The idea is to have the enemy fire on the missiles as they approach, then lose the salvos as the 2nd stages separate. So the enemy fleet has to fire again on the more numerous second stages. Meanwhile my beam fleet is coming into range, and whatever ASMs they fire against my fleet can be more easily stopped by my PD than the masses of AMMs the NPRs would otherwise tend to fire at my ships. Therefore, if my missiles evade the interception and hit the targets all the better, but their main reason to exist is to harrass and distract the enemy while I get into range with my beam ships. . . let's see if *this* plan survives contact with the enemy.
On the AI targeting: from what I know, they'll attack not the largest ship, but the one with the largest EM signature (shields, sensors), if they don't know anything else. Once they do know, they're pretty smart and will target your PD ships, for example. You can't make them attack a commercial design: they'll know it's commercial from the engines and will tend to ignore them while there are armed ships around.
1. I have a question about combat mechanics . . .
Do I understand correctly that the accuracy of energy and kinetic weapons is related to the ratio of the speed of my ship and that of the enemy? Accordingly, if I want to make small effective melee ships, they must be fast - presumably 7-8 thousand km / s?
Will this speed be taken into account when firing if I order my ships to get as close as possible to shoot the enemy?
the basic rule is rather between the tracking speed of your beam fire control and your target's speed. If the target is faster than the BFC tracking speed, the to hit chance is reduced accordingly. If you use boosted tracking speed in your BFCs, the tracking speed will rather be the maximum between you ship's speed and the BFC's. Unless you use turrets, when it's the turret's speed that's relevant.
