I think you are confused about how to use Kamikazes. They are used on DEFENSE only. If an Allied power attacks Japanese ships in or launches an amphibious assault from any sea zone with the Kamikaze symbol, the Japanese player can use Kamikaze against the Allied warships.
Also, in the case of amphibious assaults, a Kamikaze strike counts as combat so it prevents bombardments from Allied battleships and cruisers.
In all three of your questions, it sounds like you are using Kamikazes on attack which they are not meant for.
However, in defense, if Japan has defending submarines and Kamikazes take out any Allied destroyers, then the defending subs to get to fire in the Surprise Strike phase of combat.
Also, if a Kamikaze scores a hit on an attacking carrier, while it does not keep any attacking fighters and/or tac bombers from the attack, at the end of combat the planes will not be able to land on that carrier, resulting in their loss unless there is a valid landing space in range.
I hope this helps you.