Not sure on the points but I'd ditch the 4th warband, convert the 4 with shield in Warband 2 to Reavers and then add as many crossbows as you can.
That way you will probably win the shooting war and your squishy guys won't have to run suicidally all the way forward as the enemy will come (at least part of the way) to you.
Also make sure you have a Captain leading the crossbows rather a Bo'sun, as his Courage 3 and 0 Will will be useless once you are Broken (and his banner is useless as you won't be in combat).
Saying this as a player who's main army has been Corsairs for a while now.