Firstly, at the rate of things in Iraq and Afganistan, is there not a high probability of gurellia warfare playing the largest role for the forseeable future?
In my estimation, no. Asymmetric warfare only takes you so far; the easiest way for a state to combat it is through technological development and training. Deploying conventional military forces to fight guerrilla style campaigns is often clumsy and brutish, and that simply provides greater incentives to devise technologies, tactics, and forces designed specifically for the purpose of eliminating guerrilla elements. In the meantime, states also continue to confront the possibility of direct action against their peers, which has been and will continue to be the major threat to their existence; a terrorist group is generally incapable of destroying a distant country, and is at most something of a random, deadly menace. A state's military is a different matter.
Second, what sort of unit and circa what point is the Gunship air unit supposed to be?
The modern sense of the word, specifically as relates to vehicles such as the AC-130 and its predecessors, and its likely descendants (a major current aim is to develop diode versions of the Airborne Laser and mount them on C-130s for ground-attack). Helicopters which have received that designation (like the Mil Mi-24 Hind) would instead be regarded as Attack Helicopters.
Third, what is represented by Variable Attack?
A larger version of a Variable Fighter, capable of carrying a larger weapons load (be it "bomb truck," "missile truck," "laser truck," and so on, or balanced) and therefore capable of heavier and more sustained action. The term "Bomber" is no longer really applicable since it's possible with the set up and the weapons loads to produce a vehicle which is capable of defending itself against other airborne threats (and attacking them) and performing similar missions as Fighters if necessary. The classifications for direct combat vehicles becomes less about survivability, mobility, and mission role and more about relative size and firepower.
Regarding the unit listing, I do think that it may be more complicated than necessary or useful. However, this depends on the resolution of the NES - temporal and otherwise.
Where, specifically? To need something of this level of detail I think you generally have to be in the realm of one year updates--lower resolution and the detail is less important, and higher resolution and you'll never progress very far along the list.
In many cases, the presence of one type of unit strongly implies the presence of another.
This is true enough, which is why I didn't bother with support and maintenance vehicles and trainers. I included transports, tankers, and eWar birds for a few particular reasons. The capabilities represented by all of them in the Space, Aerospace, and Air categories are not universal, and their development is key to being able to conduct projection of force and battlefield dominance (the United States, for example, is the power it is because it can project its force globally--it cannot do this without its Airlift and Tanker capabilities). The eWar birds provide dominant command and control capabilities that enable a much more coordinated response against foes, which can be a devastating advantage if they do not have similar such systems. Although these advantages are not
directly combat related, they have a huge impact on what you can do and how well you can do it. I couldn't see not including them as a result. This helps distinguish the haves from the have nots and makes it much easier to assess one's capabilities in deployment and sustainment of missions.
Similar arguments can be made for land transports (mechanized infantry require having both the soldiers and the vehicles, like APCs and IFVs; motorized infantry should therefore have corresponding vehicles, namely converted trucks) and it doesn't make sense to include the detail in one field, but not in others.
Something I have noticed is I didn't really budget for Sea or Space Transport vessels.
It might be a good idea to categorize such units into groups, and simply list the number of those groups that a given nation can deploy.
I'm not sure I follow.