Etruscan Military is divided into two basic systems, both providing 5 units:

1. Oligarchic System - Small but very strong and specialized Noble units aided by cheap levy units.

2. Republican System - Citizen Soldiers, Gradually trading Armour for mobility.

plus 2 cavalry units and a Marine unit all tied to specific conditions(or skills). Also three of the basic units get replacerupgrades via Skilltree.

In detail:
1. Oligarchic System: This System is based on accounts of Etruscan Warfare Prior to 500 BC, generally identifying two groups of Warriors, Nobles doning Armour similar to Greek Hoplite Armour but weapons unfit for Hoplite Warfare, like Axes and Bows suggesting the favouring of single Combat where applicable, and Semi-free or Freed servant classes often being outfitted by a Noble.
At first only the Himiu Caceiva(Levy) is universally availible, as most cities lack the capacity to field enough nobles to fill a regiment. They are offensive minded Trash units, use them as such. - They later get replaced with Retainers, which are much more reliable.
In your Capital(and other major cities) you should have Access to Capuxva(Falcons), a small unit of Noble Archers. Unlike the Greeks the Etruscans considered Archery not below the honour of a Nobleman. They are less squishy than other Archers but still Archers and should be kept out of Melee. If you wish to train them in other cities you might want to allocate larger Estates to the local Nobility.
With the Construction of an Armoury it is Possible to both arm the Freedmen and field heavier units of Nobles.
The Leutnir(militia), basically are those people who are neither too high status to be forced to fight nor actual slaves. Their equipment is poor at best and the decision to field them in the first place is quoted by roman historians as symptom of the Decay of the Etruscan society, much like late Rome's practice of employing Germanic Foederati instead of Roman soldiers has earned it the reputation of proverbial Decadence today. They are quite weak but they can blot out the sun the the shier mass of Javelins they can lob at the enemy.
In Major cities like your Capital, the Armoury enables the Training of Leuxva(Lions) and Thevruxva(Bulls) small units of brave men in shing armour. While the Lions, armed with Two handed Axes, unusual for the era, are Ferocious chargers the latter, armed with shield and sword, are more defensive minded, tho not having the same bracing power of Elite Hoplites.(come to think of it I might swap those names)

2. The Republican System: In many ancient Societies political participation and military service were closely connected, which in turn promotes democratic tendencies in densly populated diverse regions. While often believed to be Monarchistic the Etruscan Society is likely to have developed a own form of Republic not desimilar to the Res Publica of the Tiber Valley. This is both obscured and highlighted by offices like the Zilath, which roughly translates to Praetor. Now in many ways roman Praetors were the successors of earlier Kings, sharing most of the responsibilities. What is attested is the existence of the exceedingly high office of Zilath Mechl Rasnal(the attached L indicating Genitive). Earlier believed to be the King/Praetor/bigkahuna of the Etruscan People(we don't know what Mech actually means, this is more or less the only place where is was found, it could also mean host or roast for all we know, but having a high official responsible for sunday roasts it little likely). But Most people do not call them selves "those of Steve" that's just something later generations like to make up (see Romans). In very many cases peoples endonym is something along the lines of "People", "Humans" or "men", like the Inuit or even the Germans, sometimes it's more descriptive. With that in mind Rasnal could just aswell simply mean of the People, discarding that as a possible meaning of Mechl. Now it has been argued that Mechl could mean Thing or Issue similar to latin Res suggesting the Translation Praetor of the Public issue or Res Publica or Republic as we would say today.
Now ... so much for that. The thing is that we don't really know a great big deal about the Etruscans, we can't even count to ten without causing a minor controversy, but I try to be as true to the source material and modern academic insights.

The Roster is Similar to the early latin one in that it consists of 5 classes of society with the 1. class being a heavy Hoplite and the 5. class being a weak skirmisher. This System does make a lot more sence in a Republican or Tribal society than in a Oligarchic one, due to the high percentage of (heavily) armed Citicens. The Etruscans seem to have been quite fond of Numbers(making the aforementioned uncertainty even more awkward) so I decided to forgo long composite names that tell you nothing, and just number them 1-5.
1 - Heavy Hoplite, of the Nobility, resticted to Major cities with armouries.
2 - Medium Hoplite, requires Armoury.
3 - Light Hoplite no further requirements.
4 - Light spearman, best as reserves.
5 - Light Skirmishers

With the Reform your 2s and 3s get new equipment and get more mobile.

Support:
These are all Fictive, fictive but quite likely. There are no records of considerable Etruscan Cavalry forces, but they had Horses and there were some excellent breeding grounds on their Territory, so it is to assume that sooner or later they would have some form of cavalry. Chariots are attested but there is no model and I'm quite sceptical of their Military application in this context. They were likely used mainly as Commanders vehicles. If i could I'd make every unit of Levy include one guy on a chariot giving orders. Light Cavalry can be trained basically everywhere were there are suitable horses, Heavy Cavalry however requires an Established Nobility, Armouries and Warhorses in addtion to the Military Reform from the Military Tree.
Similar to Noble Archers, Etruscan Marines are good archers, with decent melee capacities, however this is due to their mixed nature, which should be almost equalled out by their greater unit count. They do have superior Attack and Charge to making them a bit redundant in an Oligarchic army but quite usefull for the Democrats. They require a shipyard to be built. Marines are not seperately attested, but as the Etruscans are known to be decent seamen and neither maneuvering nor construction seems to have been their strength compared to Greeks and Phoenicians so It's fair to give their "boatmen" a slight edge.