Hopefully this will help most of you to choose units that fits your needs.
Feel free to signal any mistake and do not hesitate to let a word of thanks to bringback this subject on first page.

How is damage calculated ?
Most tanks carry both kinetic and HEAT shells. Some vehicles only carry HEAT shell. In that case this is specified in the calliber line of the unit description.
I begin with HEAT since it's easier :
Heat amunition have an anti tank value (AT) and and anti infantry value (AI).
To calculate how many damage you will deal to a vehicle you do the simple math : AT power + 1 - Armor value
If there is no armor : ATx4 = damage
Damage versus infantry is the following : for a good hit you kill as many soldiers as you AI power. Sometimes you gan get a near miss and still kill some soldiers.
Tanks with kinetic shells also have HEAT shells that re not displayed and they only use them against infantry.
Kenetic shells power dipends of the distance. The AT value displayed in the unit specs correspond to his AT power at max range. We often refers to that as Armor Piercing value (AP).
The damage dealt by kinetic shells is the same as HEAT : AT power + 1 - Armor value the only difference is that your AT power increase by 1 every 350m. See the chart to see the full list of ranges and their AP bonus.
Veterancy increase moral recovery, accuracy, critical hit probability and the possible amount of damage dealt by the critical hit. You can find how veterancy affect accuracy in the chart.
Accuracy vs infantry does not portray reality because infantry dies to area of effect damage when the shot is a near miss.
Stress reduces accuracy and rate of fire. See the chart for more info.
Unit size affect only received accuracy. See the chart for more info.
Supply vehicles carry a fictive unit of measure that I call "supply point" this unit of measure is wrongly called Litre in the armory. It is not related to the fuel you put in your vehicles with a ratio of 1. See the chart for more info.
7,62 MMG and infantry rifles only engage targets with 0 armour.
12,7 and 14.5 HMG engage targets with 1 armor and damage them very slowly.
12.7HMG stun faster than 14,5 because of the low rate of fire/accuracy
Units speed listed in the armory correspond to their of road speed.
There are 2 speeds on road : tracked vehicles = 110kmph, wheeled vehicles = about 150kmph
Cover reduce the speed of vehicles : -50% for wheeled vehicles and -33% for tracked vehicles
Fuel consumption is time related not distance related. Moving through cover cost more fuel and roads allows you to spare fuel.
AP power scale with distance for kinetic weapons : you gain 1 AP level every time you reduce the distance by 350m.
Under 350m any kinetic AT weapon that couldn't normaly penetrate an armor will penetrate it and deal 1 damage.
Arty minimal range is :
Abbot : 700m
Smerch : 6125m
Uragan and MLRS 5250m
BM21 and RM70 : 4375m
Everything else : 1750m
Buratino : 525m
AuF1, Paladin and Dana : 175m /!\
Anti Air Artillery range vs ground target = 1226m
StarshipE2, MBT70, Kpz70, AMX10P milan are able to shoot with the autocanon plus their gun/ATGM at the same time. TO55 and TO62 can shoot with the gun and the flame-thrower at the same time.
Weapons always use their HE value against air target.