To answer all of your questions, planes and submarines cannot attack each other unless there is a destroyer. Period
submarines hits can NEVER be assigned to planes, destroyer or not.
I don’t have a rule book handy.
Can only 1 mec blitz with 1 tank, or it doesn’t matter how many mec blits as long as there is 1 tank?
1:1
The only exception to 1:1 is, I believe, any number of planes attacking subs when one destroyer is present. Otherwise, each of the mech/tank, inf/art, fgt/tac, and tank/tac bonuses are 1:1.
Your right sir Bombs alot. Planes vs Subs w destroyers should be a 1:1 Ratio.