I like to use the army on Crete to conquer Crete... that gives you another nice safe source of income (naval trade rules) that needs only a 1 unit garrison. After that your main mission is to take Corinth by hook or by crook. Once you hit that magic 5 province number you should be secure and actually from then on it gets increasingly easy as Classical hoplites + Peltasts = win versus phalanx based armies.