[Summary by Kay-Arne Hansen: Anyway, I asked how big the Iron Fleet was. And this was the answer he came up with. I do not recall how many major lords Balon has under him, but I think we speak about a fleet counting perhaps a thousand ships. (but only small ones :)
Oh yeah, this is just before he goes touring - hence the comment about his rush.]
No time for a lengthy answer. I leave town tomorrow and there are a million things to do.
In brief, though... the Iron Islands can float a lot more than a hundred ships. Each of the major lords probably commands that any.
However, it is important to remember that the longships are smaller and simpler than the fleets that Joffrey and Stannis warred with on the Blackwater. The former are Viking longboats, more or less; for the latter, think Venetian/Byzantine dromonds of war.