Have to agree with Ashen. A big navy gives a much larger array of options for raking in the florins and launching attacks. Staying relatively small and grabbing one or two of the three trade goods provinces (like Sicily, Sweden etc.) through a bit of a surprise overseas visit is key to success.

Heading north into Toulouse or Aquitaine is often eased by the French and the English kicking the stuffing out of each other and ignoring you until they are too weak to resist.

I am a bit disappointed by the boring GA campaign objectives for the Aragonese (in High anyway). They don't seem to have anything to match the hilariously mentalist Krak De Chevaliers objective the French have in Early (it's possible that few factions do).