1) On the Weapons page of the Gameplay section of the main GOIO website there is a
table with weapons stats, including the range of the AoE damage. Unfortunately the table is broken at present. If you hit the baloon with a carronade shot, the direct damage is done to the baloon, the AoE damage is done to the baloon and every other component within the AoE range of the hit. There's another
table shows the damage modifiers for each damage type against each component type. Your damage does not go to waste. If you destroy the baloon you get pass-through damage which is dealt directly to the hull and bypasses armour (that's my understanding, a Dev can confirm).
2) Check the damage
table to see the modifier for Explosive damage against the armour (x0.3). A direct hit to the armour is doing 0.3(60+20) = 24 damage to the armour. If you were on a Pyra this is why you'd pair a hull damaging weapon like the Scylla with an armour stripping weapon like the Whirlwind.
3) To damage the armour/hull aim at any part of the hull other than the baloon.