How does damage work?

So lets get it started. Will get mathy a little bit, with my questions.

1. I have a strike weapon with an attack value A.
I do A-D damage
where D is enemy defense against strike weapons
Is it that simple?

2. I have a strike weapon with fire damage. "As" is strike atack rating, "Af" is fire atack rating.
I do (As-Ds)+(Af-Df) damage?

where Ds/Df is strike/fire damage.

3. I have an atack rating of 200, enemy has 100 defense. I have a 50% bonus.
I do:
(200*1,5)-100=200
or
(200-100)*1,5=150

4. Backstabs, riposte, leo rings boost only physical damage?
Tearstone ring, Power Within.. boost all damage?

5. I do 500 AR, hit an enemy with a shield 90% damage reduction and 200 physical damage reduction.
I do:
(500-200)*0,1 = 30 damage
??

First off, the listed value for the weapon is not damage, its Attack Rating, which is different.

1. No

2. No, though each AR would have to go through their respective defenses yes (which is why elemental weapons deal less damage than +15)

3. I believe in the case of a 50% bonus (not a bonus equal to 50%, different things) like from the RTSR) its (200-100)*1,5=150.

4. Partially correct. Crits (backstabs and riposte's) multiply the weapons unbuffed AR, wether magic or physical. Any additional damage (like from the Red tearstone ring or crystal magic weapon) is added after. Otherwise you're correct. Though the leo ring only boosts counter damage, which can only be caused by thrust attacks.

5. Partially correct. Again, AR-defense=damage is not the formula (the formula is unknown,) but that is the order the game does the math in yes.

It's not so simple.