Sorry.....I lol'd.
Ahem, I think that sounds like an awesome mod, actually. That's how shields should work - in real life, your health doesn't get farked when a sword clunks it, but a hard hit does take some stamina/endurance out of you. I like it.
1) Err, I don't know how armor rating and shield armor rating affect damage. You could make up a simple equation that will balance the difference. Maybe the armor rating of a shield, say (66), would take 1/3 of your stamina (33 points). Then factor in the weapon the attacker is using (say, damage 20) and add 1/3 of that into staggering? I don't even know if that makes sense. You could just ignore weapon damage and use the armor rating of shields to block whatever it is that they're getting attacked with (simpler, yet still adds to realism - hey daedric shield should be as rattled by a steel sword as an ebony one....though two handed weapons this realism gets lost a little).
2) Force stagger opponents while blocking.....hmm, without a potion of drain/damage stamina, none I've heard of.
Sorry, hope smarter people can help you! Good luck with your awesome mod!