Just use the near unlimited supply of money you got to bribe everything and get stabil alliances with both the pontic and parthians....while you use the horde tactics against egypts few armies you cant bribe....

On vHard/vHard I had no problem becoming allies with all northen nabours except GCS (monitarian gifts seems to be the thing...as well as bribe any serious armies entering your territory...)and seriously whip egypt...Selucides however must blitz the Jerusalem and Sidon never allowing the egyptians to get outside Egypt for long...else all is lost...or at least very very dificult...