1) The Taras bit is a stroke of luck (in the sense that with some luck Rome conquers it within a couple of years, otherwise ...) and eventually either Epeiros or Rome make something out of it...
2) You're not alone here. We are looking for a balanced AS faction which would be more than able to hold on to its western possessions; but gradually loose it from the East. Unfortunately the Pahalava and the Baktrians do not always help this scenario by going to the Steppe instead. Again something we're trying to improve.
3) Funny you should mention this. From my AS campaign:

For about 27 years the Maks had been doing OK; even able to claim Delphi as their own private oracle... However they got a little too much into the KH bashing business (the KH who did manage to hold on to Athens btw) and the Epeirotai knew a chance when they saw it... With the Maks leaving Pella virtually unguarded it did not take long from 245 onwards for Epeiros to conquer Makedonia. A similar pattern assured the fall of Demetrias and Thermon.

It's more a case of 'classic' AI failure to recognise the need for decent border garrisons + Epeiros building up armies for decades; rather than a balance issue. (Because for 27 years the three Western factions almost perfectly held each other in balance- and had the AI not decided to go against Athens' big walls yet again... This game could've continued for another 27 years.)