Thank you Durk for the answer - was not that sure I will get any.
So legions are my core units obviously. How do axilliaries complement them, what role do they play with maximising the battle results? Do I look at the traits the elements in the unit have in order to see what they are good for or are there roles for units that are not written in their traits and I need to find information about them elsewhere? Do axilliaries play some sort of a role as screens, flank protecters to the main legion units, or are they used in rougher terrains and have bonuses there where legions have penalties?
For saggitari (archer) units I would deduct that they just soften the enemy in the fire phase before the melee phase but how much is their effect seen in the game - is there a substaintal difference in battle results when you add them to your legions?
Cavalry unit added with the legions army functions as "eyes and ears" of my army so that enemy units in neighboring regions have a harder time hiding from me and I am beter able to see what their unit composition is? How do you employ them as an independent delaying force, can you give me an example? I send one cavalry unit towards the suspecting approaching enemy and when I encounter them I put them in what battle stances in order to pull out a delaying tactic? In what instances do I need independent cavaly unit as rapid moving force - what do I seek to gain with them if they can't conquer settlements?
A hailstorm of questions, I know.

Will make me appreciate the game much more when I will understand how to properly assemble and use my armies and it might help someone like me who returned to playing this awesome game.