How many warships do you think the Vale can throw in a war? The Stormlands? The crownlands? Could all of these combined be a threat to Braavos?

I think the Vale’s fleet is pretty small, especially after the Battle of Gulltown in the Conquest and the Stormlands fleet is smaller. 

After the destruction of the Velaryon strength, the Crownlands can pull together ~10 warships. Really, only the Royal Fleet, with its 200-odd warships, could be a threat.