The Latins, currently only represented by the Romans have access to a good lot of all-purpose heavy infantry, lacking both Archers and decent Cavalry. Their native roster depends on their Government(Tribal Oligarchy or Republic):
Oligarchy grants few specialized Units, they cannot be upgraded.
Republic grants a ever evolving roster of medium to heavy Infantry.
In addition they can train Allied Units in non-Native Settlements, that are not otherwise availible to these Factions, once they have unlocked the appropriate Skill.
They are great at assimilating other Peoples with their Unique Building, the Forum.
They have very poor naval traditions, but they can Unlock special ships that can hold more Troops in excange for speed and finesse. So in order to have any relevance on the ocean they will have to advance quite a bit and then force the enemy into boarding battles.

The Etruscans rely mostly on heavy Infantry but also have a few other Troops worth a look. Their roster is split between Republican and Oligarchic Governments both having a few Upgrade Options.
Oligarchy grants access to Heroic Nobles in heavy armour fighting in very small detachments.
Republic grants access to a decent selection of Infantry.
In addition to granting Local Autonomy Etruscans know how to superimpose their own Nobility onto client Peoples granting them more profitable Autonomy Options.
They have decent naval tradtions, giving them a decent start, but they do not significantly improve later on. Holding the Water as Etruscans is neither especially easy nor difficult, but it is something that has to be constantly tended to.

The Sabellics are a wide Array of Peoples, and thus also have Access to a wide Array of Troops. Their Roster is largely dependent on the Settlements location and the Subgroup(Islander, Oscan, Umbrian), some Factions even field a few unique Units, like the Samnites and Campanians. Governments also have a small influnce on Troops selection tho, leading to a large number of possible rosters.
Like their Roster many of their Troops are Flexible.
While Islanders have access to an extra early shiptype, the Sabellics are not great Sailors, and they should better use Subjugated Greek naval capacities instead. Early supremacy might lead to latter domination under a skilled Admiral.
I also dumped the Sicilians making them Sabellic groups with the Islander Attribute and increaced amount of greek trade present in the Region giving them access to Greek units fairly early. This retains their Identity but gives them more focus, as their troops divide between swift raiding units, hoplites and the common Sabellic Elite troops.

The western Phoenicians, or Punics, have only limited Troops at their disposal, many of which require access to shipping, tho their other requirements are rather modest. They do however get several reforms, resulting in an ever changing and adapting Roster and their Archers and Cavalry are rarely surpassed by the Italic Peoples, the access to African Elephants being a good argument for them having the best Cavalry in the game.
To Augment their Roster their abilities to enlist Mercenaries is boosted.
In addition to regular Autonomy they can limit their influence on a Settlement to a trade embassy, which is both significantly cheaper and can be established much earlier, at the cost of not assimilating the settlement.
Their Navy is of superior quality, being sturdier and boasting more cargo capacity. Unless they are carefully observed they are capable of taking the Sea at any time.
They too are currently only represented by one faction, the Carthaginians.

The Greeks have a rather focused set of rosters, there being multiple variants of Hoplites, Peltasts, elite Hoplites and cavalry. Their Unit selection is entirely dependent on their Political system, of which they have a wide array available.
Rulers, generally come with better equipment for Cavalry,
Egalitarian societies boast better standard Infantry, while Hierachical ones produce superior elite Infantry and Cavalry.
In additon there are a few local Unique Units. Unlocking Hellenism will replace large portions of the Roster and is especially profitable for monarchies.
Thanks to their Unique Buildings they Unlock Skills quicker and they have more Skills to unlock as well.
Their Navy is of superior quality, boasting superior speed the ability to build ships even bigger than their Contemporaries. When given enough resources and some enemy negligence they are capable of taking the Sea at any time.

The Illyrians don't have the large variety of "heavy" infantry of most of the other groups, their Military is focused on Peltasts and Cavalry instead. The main lines of division run between Coastal people, with Marines, and those inland, with Cavalry, and Iapygads from Apulia and the "Dalmatians"* from the northern shores of the Adria. Generally however they fall in the "old" pattern of Egalitarian governments promoting Heavy infantry over Cavalry and rulers enabling Elite Guard units.The Illyrians have a long History with their Greek neighbors and profit by far the most from their Culture making this skill a special priority.
In addtion to "normal" governments, Illyrians can just let their cities ungoverned with the "Anarchia"-Upgrade severely limiting it's output, but doing wonders for the settlement itself.
Their Navy may not boast the Huge Warships of other peoples but their smaller ships are Superior in most situations, as they tend to be quicker as well as Cheaper without being less hard hitting. Ideal for raiding and hit and run tactics. They will be more than capable of taking naval superiority early and are well equipped to quell any budding enemy fleet before it can accumulate sufficient power.

The Gauls roster is balanced between Uprades and Governments.

Their Navy is not quite on the same level as that of other Peoples, lacking both large ships and any ramming vessels. They do however easily defeat Latins and sabellics until these get their hands on Greek designs. Taking Naval control early is imperative if they are to ever control the seas. Even then It will take a Skilled Admiral to ensure it stays that way.

*Offcourse neither Histri nor Veneti are Dalmatians, but considering the former are just barely Illyrians and the later are certainly not, i think it's fair to use this as a group term for them anyway. bonus: Invading Illyrians can be of this group.