I don't think adding officers for the sake of adding officers is a good idea if they're not functional, that'd just result in unnecessary bloat and make your roster harder to navigate. All the lower officer positions are abstracted with unnamed NCOs anyway and it'd be weird to have named officers occupy and leave them as they please (i.e. whenever a new assignment for them is created) without any impact on ship performance whatsoever. I like detailed assignment histories myself but they tend to happen naturally as your game grows older, mine currently has ~2700 naval officers, many of which have served on 4 or 5 different ships during their careers.

Player-designed command components sound interesting, and I think it'd be nice to have an option to have miscellaneous officers with your miscellaneous components, however making them actually apply their bonuses would be a natural next step, and I'm not sure how easy would that be code-wise, or balance-wise (let's say their efficacy would depend on component size, would we use the 1 HS AUX or the 4 HS PFC as a baseline?). So I think miscellaneous command posts would make for a fine roleplaying addition, but the actual, functional command modules are best left as dedicated, researchable components.

Of what C&C modules to add, there's not many that come to mind. By far the most necessary ones, in my opinion, are ones affecting the ship's strike group's Reaction and Fighter Combat. More on this here, but in short, there's no way for fighters to actually take advantage of either of these bonuses en masse, while the former can often make or break a fight, and the latter being useless simply feels like a waste.

A similar module affecting the ship's boarding troops (or even the ship's strike group's boarding troops) would probably be interesting as well? Could be an interesting exercise in having GU commanders operate on ships too, could be extended into a full-blown Ground Force Headquarters module as part of the GU hierarchy.

A military-only Logistics module could be useful for massive combat ships that take many days to resupply, as a compact alternative or a supplement to cargo shuttle bays. This sounds dangerously close to the previously-proposed indsutrial command modules that Steve decided against, as adding them to a design would be a no-brainer, but making this module military-only would relegate it to a rather narrow capital ship role. Could affect ordnance transfer rates as well, I suppose? But that's about the extent of my imagination as of now.

• System Governor as another Admin level between sector and planet.
• Return of Tour lengths for automated assignments. So captains can have a couple ships underneath them before assuming a flag rank or Junior Officers can experience support/fighter and other roles before getting a major command
• Ground Force Admin Commands as beyond the Division level, it's impractical to create HQ units and the user may want to spread the Corps or Army Group between multiple bodies in the same system.
• Ability to retrain officers from Fleet/Army/Admin/Science to another type of officer, Mostly for Roleplay or to quickly increase officer numbers in one category. i.e. your overmanned on Administrators but have a pressing need for ground force commanders or your ground forces are small and you need to find a propulsion MacGyver among your grunts.
• Ability to designate a Fleet/Ground positions ± 1/2 rank for assignment would be a welcomed addition.
• Reintroduction of Staff Officers for admin commands. maybe just 2 positions but you choose the boni they will provide.
• Reintroduction of Missile Series system

Huge, huge YES for Missile Series and System Governors, I would even speak in favor of adding a Sub-Sector Command as an early-game low-range (1-2 jumps max) command building and an Empire Command as a late-game empire-wide command builiding, while relaxing the necessary installation amount for large sectors to make the Sector->Sub-Sector transition work better. The NAC system we have now is awesome in how detailed the hierarchy can get, and I'd love to have something similar for civilian administrators.

Tour lengths coming back would be very nice, but clicking the naval reassignment button once every so often provides the same result. I agree that having it happen automatically would feel more natural, but only if adding exemptions (per-ship and possibly per-class) is possible too. As for multi-planetary army groups, I've never been in a situation where I'd want to maintain a massive army on several planets in the same system at once, but having some way of extending the GU hierarchy into space would be interesting, perhaps with a possible GFHQ ship module previously mentioned.

One of the closest things to decoys used on modern ships is Chaff, which is a lot of very small things to confuse incoming missiles. So smaller decoys make a degree of sense. Aside from a small number of air launched drones I am not aware of any decoys which do try to match the signature of a real vehicle.

Not a Navy example, yet nearly half of the russian long range drones currently launching at Ukraine every day are Gerbera type, which are mostly decoys, mimiking the main long range strike drone type (Geran-2, the russian licensed copy of Iranian Shahed-136). Gerbera type radar signatures are artifically enlarged to match Geran-2.

Modern flares are mimicking the actual engine signature in wavelength, not just heat, to fool heat-seeking missiles as their homing heads have gotten increasingly sophisticated. And decoy drones, most of which specs are secret, are trying to mimic the sensor signatures of real planes or ships. Same with sonar and submarine-launched decoys.

Decoys can be any size. A few, smaller decoys would give you more flexibility if want to lessen a strike rather than commit everything.

I think the confusing part is that there appears to be no reason, mechanically, to make decoy missiles that match the ship size, or in fact anything larger than the minimum decoy size. As far as I can tell, only the total mass/signature of decoys determines the fraction of missiles deflected, and cost scales linearly for both decoys and launchers.

Intuitively, I think players expect a decoy to "look like" the ship it's decoying from, i.e., to have the same signature. I can see why the actual mechanic is different, as its more flexible and less micromanage-y than requiring exact size matching (plus avoid issues with ship sizes that aren't nice, round numbers), but the fact that an infinite swarm of size-5 decoys is arguably optimal (same performance and cost as any other option, maximum flexibility) seems to eliminate what could/should be a gameplay decision point.

I thought that only decoy missiles with the correct signature will defend a ship.  In other words, a 20,000 ton ship must be defended by decoys which each have a signature of 20,000, not multiple decoys with signatures that add up to 20,000. 

Hmmm...after reviewing the section on decoy missiles I can't rule out your take on it, or mine.  It isn't clear.  Arguably your take is better given the limitation on decoy launcher size, but that could be an oversight.

This way would make more sense to me as well. However, my observations of NPR designs is that they don't really match the decoy size to the ship size, and I assume Steve would not deliberately saddle the NPRs with an unworkable design feature.