I've played Seleucid VH/M and I usually leave the Levant alone until I've full developed. I focus on obtaining VC territories that are owned by other culture groups, so I don't have culture penalties before they become huge cities. Funnily enough this causes me to hit Greece right after I deal with the Palahvans. I take Rhodes, Halicarnassus, and Sparta before I make a quick peace with KH, then I spy on Mak cities looking for those close to Huge city status

The Pahlavans are almost never a true threat. Spam of about 10 phalanges are usually enough to exterminate that faction. It's a simple matter of extending those (on huge unit sizes) phalanges all the way across the map and then walking to the other side. Catch a horse archer and maul it, move on. It's positively unfair how resistant levy phalanges are to missile fire.

For some reason since I didn't make any aggressive moves the Yellow Death was surprisingly docile and never sent a full stack against either Damascus nor Antiochea (let alone attacked those two provinces). I have no clue why but I enjoyed it nonetheless.

In ALL my Seleucid games this is almost always a constant. Hayasdan is almost never a threat as they primarily expand north. Once their primary armies have expanded enough it's a simple matter to take their cities in Caucasus. Baktria is never a threat as they rarely ever go into India and I don't war with them; they have the same culture group I do, so I let them develop for me and deal with the Saka for free also.

Pontus for me has been a wild card however. They are never aggressive against me, but usually they stick to one or two provinces. On my last playthrough they took over most of Northern Greece before I declared war on them (their capital had 23,000 people or so.) Would've loved to see the rest of their expansion as the Maks were stuck to Epeirote and Thrace while the Epirotes themselves were stuck in Illyria.