what id do will be best in the interest

first u gift ur chersonesos area to makedonia but first destroy all EXP building and the goverment
leave the rest alone to the makedonians so they wont keep rebelling to u
this will cause the makedonians to resurge a bit
in the meanwhile gift them from 5000-10000 gold per turn so they'll survive and also improve there view of u (if u gift a faction money, no matter how much, less chance of them betraying u)

next is to try to contain the baktrian power engine
move there armies (command move_character "Captain Antiochos"etc) back to the east, thatll slow down there advance and leave there cities open to attack
and since there armies are far away, the ptolemaios and etc can attack on better grounds

If u can abandon arse to a faction thats greek but also friendly,
Id handly put Epirotes or makedonians there
just to keep the roman/gual from pushing into iberia or vice versa

then a question
do you plan to fight against the "barbarian horde" or the civilized "eastern despots"

from what id do if i was u after the above
id id conquear Nikia and split the pontic lands farther and conquear anatolia down to the ptolemaios and focus ur war to the armenian lands

then its all fun wars there :)