No, I haven't had this discussion unto boredom.

And yes, you make some valid points. Very valid, and one or two I've not heard brought up before either.

As a wannabe S/F writer I have studied this subject more than most. Some folk here have seen my versions of this as fiction, but with FTL. Right now I am abbreviating my reply. time factors.

There are two ways to approach the subject, each is very distinct and different in tactics and strategy.

One, without FTL, slowships, maximum realistic velocity, 70 - 80% of C.

Second, With FTL, then you have an entirely set of parameters to work with, and around.

For the time being, let’s limit this to slowships. Which would be a very long drawn out process, decades long at best, more likely centuries.

If you are limited to STL you’ll have to take an extensive manufacturing and maintenance base with you. Which wouldn’t be as much a problem as you might think. STL ships will be enormous anyway, the easiest method of obtaining a hull would be to hollow out a good sized asteroid. Several of them in fact, then fill them with ancillary craft. Supplies, people and a lot of fuel. A helluva lot of fuel.

Logistics, you take it with you, or do without. Plain and simple, no way around it. A great deal of your personnel skillsets would be people to extract raw materials from whatever could be found. No matter where it is. And most likely under fire.

Approach vectors at narrow angles near lightspeed; Smart missiles, explosive warheads firing a spread of shaped shrapnel in the path of the opposing ships. No need for fancy explosives or nukes for the most part. Fire and forget. The combined velocities would make a wad of used gum more powerful than the biggest fusion device you could build anyway.

Sensory devices. Mass detectors, put them a goodly distance forward and globed to side of the main fleet. I have no doubt that by the time the technology is advanced enough for the human race to build interstellar ships we will have at least a usable form of gravity sensors. I shouldn’t need to point out G waves ignore Eienstein’s equations. You rear is covered by Einstein, no way they can catch you. Well, let me add this much. If they can catch you from behind, you’re toast anyway. They have better toys than you do.

Approach vector nearing 90 degrees, then it gets tricky. The combatants would have a very narrow window of opportunity. Same weapons though. If the approach is near enough, then energy weapons. Though I seriously doubt warfare on this scale and speed would see much use of the good old Star Wars shoot-em-up.

There wouldn't be much maneuvering at realavistic speeds, it may well be possible both factions just miss each other out there in the Big Deep. Then they find, and attack planets, mostly throwing rocks, big rocks, real fast. Why waste energy with a wimpy lil ol gigajuole laser or terawatt plasma cannon when you can take out half a hemisphere with one rock?

The current story someone else and I are co-writing has the main scenes other than actual combat located at a forward repair, resupply and refit base. Anyone who’s been in the military knows very well that RRAR is the core of any campaign. Doesn’t matter if you have the latest and greatest beenie flip, if you can’t get a new rubber bands or beans for it, ain’t much use.