most of the times the pahlavi attack the seleukids right at the start of the campaign support the pahlav instead of the seleukids they always betray you anyways so if the palahv organize a good attack on the seleukids they will left unprotected most of their settlements specially the ones on the south of baktra, your armies will consist mostly of persian archers and persian/spearman archers with some pantadopoi phalangitai this will any army the arche will try to send as soon as you feel you have taken enough from the seleukids try to get the settlements in india, just remember to bring a lot of sphendonetai to take down the elephants and well leave an army taking care of your home territory, and after taking the indian settlements it will be a boost to your economy, after that just give tribute to the pahlav so you wont engage in a war with them and just focus on the arche, they will throw you stacks and stacks of either mercs or regional units with kleruchoi phalangitai haha you can easily take them with archers and some pantadopoi phalangitai, i hope this helps, it help me though!