First, after the first engagement of the 3rd Light Armoured Company there are no more references to Hellhound tanks. I presume this means that the 4th Company was pulled back behind the lines and kept out of combat. Rather unsurprising given that the 3rd Light evaporated on first contact.
They were still engaged. I think they were mentioned in one of the last breakthroughs.
Second, casualties were fairly even between the infantry and the armour. Normally you see larger casualty counts among the infantry. This may've been the result of the relatively poor armour of the Imperium compared to the enemy's weapon strength. There's just a point where it's impossible to kill a target more dead even if you put more energy into it, and you get to that limit much more quickly with squishy humans than with the armoured shell around the squishy humans.
Not sure what you mean here. Only a small number of tanks (45 Leman Russ, 34 Hellhounds, etc.) were lost compared to thousands of infantry
Third, specialist forces suffered disproportionate losses. It's kinda hard to tell how significant that is among the armoured units, simply because there's fewer of them in numbers so an unfortunate loss of a single Vox Vehicle would skew the ratios considerably, but while Guardsmen suffered about 13% losses, Chimera saw 22% losses, Lascannons 41%, Hydra platforms 20%, vox casters 42% and Regimental HQs 75%. Infantry supply vehicles lost 11%.
That is the nature of the system. Infantry is squishy but individually small, so a single hit on an element with 2400 infantry causes 0.042% casualties. The Lascannon (for example) is an infantry-based light-anti-tank weapon, which is larger than infantry but just as easy to kill. So one hit on the element with 100 Lascannon would inflict 1% casualties. The regimental HQs are very large and also easy to kill. This is why I introduced the new rule about non-combat units. I will also be designing some HQs with a lot more armour.
Fourth, Logistics units casualties would indicate that less than 450 supply units have been lost. I take it that supply use is not counted in the casualties. As that would explain the discrepancy of 3 entire regiments of supply units getting disbanded to build everything back up to strength.
I was a little loose with my description of 'casualties'. A small portion of the destroyed supply vehicles were actually consumed, mainly in the armoured forces as they were drawing on their own supplies. The majority of the consumed supplies were in the 'Corps Assets' formations, and those supplies were replaced by the logistics formations
Fifth and final, in reality the Valhallan, Mordian and Paragonian regiments wouldn't have been disbanded, they would if possible have been rotated back home or to another secured location where they could rendezvous with and integrate reinforcements.
You can choose to do that if you wish. I didn't actually use up all the infantry in one of the disbanded formations, so I renamed it the 1st Replacement Regiment so it can fulfill the above function. Also, some units will be combined in wartime rather than rotated home.
And speaking of reinforcements, is there a 'Rebuild to Template' order for ground units? I can't find it on the wiki, and such an order would be helpful with rebuilding units that suffered casualties or replacing equipment. It would be reasonable for it to cost less in both minerals and time, simply because you are scrapping already processed materials so you can reuse at least some of it, but the time savings are notably smaller than the mineral savings and as the technological gap between the old equipment and the new equipment increases the savings grow smaller.
That doesn't exist at the moment, but it might be possible. Once constructed, ground formations don't have a template, which means they can grow, shrink or change over time. If you want replacements, you can build them and drag-drop onto the existing formation. The Race maintains a list of current templates, so it might be possible to have a ground formation 'fill in the gaps' to match one of those templates by assigning it to a training facility.