Pontus is fine as long as you sign an agreement before they cross to your territory. You must keep your eyes on everyone, despite solid alliences at the beginning, (in my game) macedon, daicia and sycthia attacked me, breaking my allience. In fact, only the pontic people stayed true. It really helps if you ally wiht the greeks (after taking some of their good territories :) ), as this surrounds the macedonians for an easy kill. Their cavalry are your main problem, as your phalanxes are hard to get and nowhere near as strong as the macedonian ones. You need numbers to succeed.

I'm currently working on getting rome allied to me so i can pound daicia and sycia in peace!