Having fought a 30 year long war with the Romans in Italy as the Epeirotes, I have some minor tips to give, though most have alrady been given by others.
My main army always consisted of 2 Pezhetairoi and 2 Phalagitai Deuteroi to act as the main battle line. Supporting these troops were 2 units of Thureophoroi, or Thorakitai when possible, plus 2 heavy Samnites, 2 Lucanians, 2 Toxotai and 2 units of Hoplitai Haploi. For cavalry I had just two units of Tarantines. Commanded by Pyrrhus son and his huge bodyguard this army destroyed dozens of Roman legions, while requiring minimal retraining.
The tactic is quite simple, the Phalanxes in the middle either advances on the enemy or waits for him, depending on the situation, while the Toxotai fires upon him and the Tarantines and Lucanians advance to throw their javelins.
As soon as the main enemy force has engaged the phalanx (it always does) it is doomed. Often some enemies will be chasing after the Lucanians, and in that case the Lucanians turn to face them while the Samnites and Thureophoroi fall upon their backs. These isolated troops often route quite easily, whereafter the Lucanians and the heavy infantry march upon the main enemy who is vainly trying to break the phalanxes. The Hoplites have already marched up on the flanks both the lengthen and strengthen them, while the Tarantines and Generals bodyguard has usually driven off any nearby missile or cavalry troops. By now the enemies attacking the phalanxes will be sufficiently tired and disheartened by their fruitless attempts to break the wall of pikes, and so when the the combined mass of the Lucanians, Samnites, Thureophoroi, Tarantines and the Generals bodyguard all hit them in the rear all but the most elite troops will rout, and these are quickly disposed of by the now massive numbers of soldiers surrounding them. If during the battle any cavarly attempts to flank the phalanx and attack the Toxotai (the enemy FM often does this) one or both units of Hoplitai´s turn to face him while my FM line up to charge him in the back, often resulting in an early loss of the Romans FM, very helpful later on when the main attack commences. If the Toxotai are attacked it is of no great concern, as they can hold their own for some while against cavalry, and are easily retrainable. Apart from possible losses amonngst the Toxotai this tactic enabled me to defeat equal or superior Roman armies while taking extremely few lossed, almost always under 50 men were lost while more then 2000 Romans often fell. Plus it´s quite a cheap army, with relatively low upkeep.
As I played this on 1.0 I didn´t use any Bruttians, but my limited experience with them suggests that I would not use them were I to attempt a new Epeirote campaign.
Damn, this got a lot longer then I expected.