A few questions about Sneak\Invisibility and Weapons

[Rubnik]

How does Sneak work? What bonuses do you get when you attack while sneaking and do they apply on auto attacks or also spells\abilities? Does invisibility provide different bonuses?

Also, do different weapons provide any bonuses? For example in Skyrim daggers dealt less damage but had higher attack speed, and you could get extra bonuses when speced into specific weapons.

I read on esonightblade.com that a headshot with a bow will deal more damage than a body shot, and also daggers have bonuses to damage done while undetected. Are those true?