First, when using stealth, how exactly does one make use of "stealthy movement"? By having a high stealth skill, does that alone make you harder to detect, or does crouching have an effect on this? Also, backstabbing - how is this done, exactly? Does it literally imply having to sneak behind an oblivious foe? Can you "backstab" an oblivious foe from any direction? Can you backstab a foe that's aware of you if you can maneuver behind it?
Stealth is checked whether you are running, walking, riding, swimming, jumping, whatever. Doesn't matter how you approach an enemy, once you get in range your stealth is checked. How successful you are depends on your skill
and how fast you are moving. So while you CAN do a stealthy-sprint if your skill is high enough, you will be much more effective if you move slowly. Other than walking, there are two ways to slow yourself down: sneaking and crouching. Sneaking doesn't add any other benefits other than that which comes from moving more slowly. Stealth-crouching is theoretically the best way to go, but has the added danger of having to not only release stealth but hit the uncrouch button as well if you have to run away.
You get a chance to backstab anytime you strike someone
in the back. Be default, any creature that is not aware of you will have their back to you when you approach them (of course, if you move around to their front, they'll probably see you). However, even if they are attacking you and turn their back to you, you can hit them and try to get a backstab. This is great like when they get stuck on a corner and have to retreat and try to renegotiate the turn, you can stick it to them as they turn away.
So backstabbing is just about hitting them in the back; it doesn't matter if they know you're there or not, it's just a lot easier to do it stealthily, as they automatically start with their back to you. Also, I've found that backstabbing is really easy to do with a bow--if they aren't ware of you, your first hit pretty much always scores a backstab.
Secondly, regarding magicka, does armor have an effect on how efficient it is? Is it possible to play as a pure mage, without having to resort to weapons? In the spellbook, where you select your spells, there's an icon that changes as you click on it. What is the purpose of this icon? Lastly, how does one cut down on the amount of "saving throws" made by enemies to totally negate your spells? Does it take a higher INT or WIL, or is it all a matter of chance?
Armor doesn't affect stealth or spellcasting. Is it *possible* to play as a pure mage, but I don't know of anyone who's successfully done that without resorting to exploits. The icon you can select just changes the icon it shows on your screen while it is in effect (so this only matters for duration-based spells you cast on yourself). As for saving throws, it mostly has to do with the monster itself, as each enemy has their own spell resistance.