with KH (After uniting Hellas under my rule) I started kickin Seleukid butts with mid-size hoplite armies supported by peltastai, cretan archers and thessalian/xystophoroi cavalry. This way I also took out Pontos and pushed the border to Trapezous / Ani-Kamah / Antiochia, just to hold the Seleukids at bay. My defensive armies there was substantially a bulk of thureophoroi mixed with local troops (cappadocian hillmen, asian riders and the amazing caucasian archers) and the border was practically unpassable :D

Then I formed my western army to expand in southern Italy, Massilia and the two Spanish provinces... and that was exentially top quality hoplites (epilektoi, tarantinoi) + KH phalanx. As flankers I used mainly Thracian, Celtic or (in Italy) Hastati. Cavarly was as usually provided by Thessalia and some Prodromoi. When Sicily was tamed, I created another army of Syracusan Hoplites which are in my opinion one of the best KH units, and used them as flankers in my conquest of Italy (up to Arretium and Ariminum).

Historically speaking, I think I would have done the same :D barbaric or semi-barbaric units (thracians expecially, I LOVE the thracians and they were my fave faction in vanilla RTW) would have made much better flankers in my opinion. Expecially against the Romans, that can hack to shreds the more similar Thureophoroi/Thorakitai. And I think historically barbaric infantry would have been more mobile too! Of course that would imply a strong Hellenic domination over Thrace, which practically never happened...