This is a dangerous strategic situation. Both Rome and the Seleukid-Pontic-Bosphoran alliance could probably easily overpower you.
We'll need to build a bigger fleet if we are to make gains abroad. This *can* be delayed if the economy is judged more important for the moment, but is definately something that needs to be done eventually.
We need allies. We simply don't have the military power to face Rome or the Seleucids by ourselves. I suggest Carthage: though our relations are bad, that can be remedied, and they would be in a good position to help us against either Rome or the Seleucids.
Continue working on gaining the Greek minors to your side - preferably through diplomacy, but if it doesn't look like that is working, use military force if it doesn't hurt your stability too much. If we end up fighting Rome or the Seleucids - like we'll probably do - we'll need all the support we can get.
Continue improving the economy whenever you can spare the resources from the goals mentioned above.
I agree with Shadow Knight that expanding further north probably isn't the best use of your resources... I'd rather see you concentrate on improving the economic output of your core provinces.
Getting into a war against any of the major powers is definately not a good idea at the moment. If the Seleucids suddenly collapse into civil war, and you have secured Carthage as an ally, it might be worthwhile to attack them - hopefully Carthage will keep anything the Seleucids can spare from the civil war busy while you deal with their ally, Pontus. Similarly, attacking Rome might also be smart if they're suffering from a civil war and you have Carthage on your side, but aside from major internal problems amongst your rivals, I'd recommend waiting for your allies/enemies to take the initiative in starting a war, rather than taking aggressive action yourself. Of course, a decently-sized fleet would help ensure the success of any foreign adventures.