Game Mechanics

Hello all, this is my first post and I have a few questions:

#1 combat:  attack and defenses, lets say for simplicity sake I have a ship with 10 attack, and 10 defense, and i get attacked by 3 ships, each with 4 attack and 2 defense, do the attacks each diminish my defense rating?

i.e. ship one attacks for 4 points -----> my ship goes from 10 defense to 6 defense, no HP lost

     ship two attacks for 4 points-------> my ship goes from 6 defense to 2 defense, no HP lost

     ship three attacks for 4 points-------> my ship goes from 2 defense to 0 defense, two HP lost

if that is incorrect...then how does it work exactly?

#2 If A ship dies in the round of a battle does it still fire its weapons one time? because when fighting the dreadlords I make ships on cargo hulls with huge attack, and no defense and even if i get the first shot, and kill their ship in one round it still always kills one of my ships? is that how it is supposed to work?

#3 Espionage: only question here is if I have 1 spy assigned to  a civ just for general spying, will I eventually reach "advanced" knowledge of the race? or do I need to have 4 spys to correlate with the different levels of knowledge?

#4 Population and Taxation: Does revenue increase linearly with population? Or is there some sort of diminishment?

i.e.  If I have a tax rate of 50% and receive 100bc from my planet with 10b pop, with I receive 200bc with 20b pop?

Thanks for any responses