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This is a pretty good summary, specifically on points 1 and 3. 
Point 2 however needs a bit of context. CM call in times for artillery are pretty spot on, for both the WWII titles and for the modern ones, for all sides. Yes, the call in times are averages, but that is a product of the CM system and really can't be helped. 
More importantly, the methodology for Soviet artillery is not the same as its Western counterpart. The way most players tend to play CM is via "recon pull" or by constantly reacting to new information and exploiting it. This roughly translates to one of the strengths of US artillery in that it is highly reactive. If you have a unit driving down a road and it takes fire from an unexpected enemy position, US artillery is flexible enough to be called in quickly against the unexpected enemy position. That is now how Soviet artillery worked, or was intended to function. 
Soviet artillery was designed to be part of a larger plan. (US artillery is too, but the Soviet application is more rigid). The vast majority of Soviet artillery was templated, or pre-planned. Even the reactionary fire. Soviet preparatory bombardments were complex and involved a constant shifting of fires from the "deep fight" (rear area targets such as command and control, logistics, assembly areas, etc) to the "close fight" (enemy defensive positions directly opposing friendly forces). The term rolling barrage is incorrect, but probably is the most relatable concept to start wrapping your head around. 
Unfortunately, CM is fairly limited in its ability to represent a proper Soviet fires plan. Under ideal circumstances, the vast majority of the fires plan would all be pre-planned missions, hitting suspected enemy positions and key terrain that moves with the advance of the attacking ground forces. This cannot be done in CM because you cannot plan more than one pre-planned fire mission per battery, and because the time delay option only goes out to 15 minutes. The best way around that is to use a lot of TRPs. There are issues with that as well though both from a gameplay perspective (covering the map in TRPs is considered gamey) and from a technical perspective (a TRP in real life is different than what a TRP is in CM in a few notable ways), but it is arguably the best workaround. 
A certified CM teaching moment! So in real life, the general rule of thumb is that all fires must be observed. Inversely, unobserved fires are useless. The reasoning is simple; if you cannot see what you are hitting, how can you know if you are in fact hitting anything? Now, there are contexts and examples were firing at a target that you cannot see is a good idea (counter battery comes readily to mind) but the key takeaway is that in CM the most effective fire missions will be the ones that you can directly observe. 

Great write up! 
I made sure to add the "personally" in there to show its my (non-professional) opinion.
In my opinion, the call in times are realistic compared to real life conbat. For example, a US company commander can call in an organic mortar battery in around 5 minutes. In real life that is very realistic but in Combat Mission that is an absolute eternity. 5 full turns! Even more if the observer has a difficult time seeing the spotting rounds.
I think we can all agree that Combat Mission moves much more quickly than a real battle would. A 1 hour scenario with the objective of taking a town would probably take three times that in real life.
That is why I think new players can get a bit confused with the call in times and I think some it's worth giving them some context.
Again, all my opinion.
 

Thanks! 
Very fair points, especially the one about CM moving faster than real life and how long 5 turns (or 12) can be in CM. I always wished there was more modularity in the difficulty levels. Something like reducing the call in times without getting borg spotting, for example. Would go a long way to helping to ease some of the gameplay quirks of the CM system, but I also understand that it would open up a can of worms too. 

Excellent responses - to add to Question 3.  So in the Soviet campaign you are facing off against 11 ACR and the 3rd Armd Division.  By 1982 we do know the early M1s (105 mm) where in Germany in small numbers in those frontline units - give or take months.  In the campaign they appear in two battles both toward the back end in what would have been US counter-moves.  This reflects that the M1s would have been held in Reserve and only used in extremis.  The majority of US armor is the M60A3, which is a pretty nasty beast on its own.  
Anyway hope that helps.  The issue with the T64 is also that the TacAI in the game always fire at the centre of mass on enemy tanks.  For the T64 that is pretty much the area on both the glacis or turret one does not want to try to target.  When playing the Soviets it does give advantage, we will get it nerfed at some point.  When playing the US try and offset.
Glad you enjoyed the campaign.

1. Experience gives a small bonus to call in time
2. The Soviet player should focus on pre planned bombardments. Personally, Combat Mission call in times are horribly slow. The Soviets wouldn't take that much longer than Americans to call in support. They just had fewer people to call it in.
3. The Abrams are there for a challenge. You're also in the most dangerous part of the front.