I have a questions. Would sneaking while setting a "Rune" trap make enemies aware of your precense? Like I want to sneak, set a rune, then attack them with my bow. So when they come looking for me they run into a rune.

So my main question is. Would casting a Destruction rune spell make enemies notice me?

yes, even with quiet casting the enemy still hears the rune being placed, and will start searching for you. then undoubtedly set off the rune. but as long as you take quiet casting and are far enough/well enough hidden they shouldnt find you.

Quiet casting? Is that a perk? Or a spell?

it is an illusion school perk, i think it requires 50 or 70 skill level illusion. it makes spell CASTING silent, but because the rune still makes noise when placed runes aren't as good as they could be.

So ultimately, runes arent worth it? I just wanted to add some suprise to my "Ranger," type character, To silently place a rune, shoot arrow, let them come near me thinking its all good, and BOOM they get hit with a good ol' trap (rune). But if i have to go all the way into illusion then i guess it isn't worth the perk points.

since you're planning on a ranged assassin it might work as long as you place it closer to you. but make sure you move after the shot, they will look at where it was shot from not from where you are. but with sneak/archery i highly doubt you'll have any use for runes unless you dont use smithing at all.
but also if you only plan perks to level 50 you still can. i usually only plan perks to 50. beyond that level all perk points are just gravy to me. unnecessary things i would like my character to have, but didnt want to put points into earlier. like i usually do with pickpocket for the extra pockets perk(+100 carry weight).

Yes i actually have dawnguard and am playing for the first time ever on the game. (Xbox) And you can get more perk points past level 50???? O_O

To answer your question, you can get up to 80 perk points max, since the level cap of skyrim is 81, and you don't start from level 0.

Thank you, and i thought the cap was level 50??? Man i'm i thought i only had enough perk points to max about 3 or 4 trees. I can easily get Illusion and Destruction trees !