Go to the Wow Warrior Forums - there are some good gear guides.

As for a purple shield, go w the 33 badge shield.

That gladiator shield is a really good viable shield for starting out (ignore the resilience thingy on the shield wall thats all )

And you shouldnt have problems reaching 490 def. Just rmbr you have 15 other slots to give you 490 def.

Btw, if you're rage starved, relook into your skill rotation.

TBH, 490 is a good guiding number, but dont have to live and die by it. I just got the ZA shield (no def rating) and it brought me down to 489).

In last nites raid (b4 I flasked), not even one crit.

Also, for resist fights like Hydross/Leo (I tank demon), I've between 460 - 480 def rting, no crits also from my recollection. Lucky maybe? lol idk..

In general, I've noticed a lot of players love to theorycraft till the cows come home as evident in some of the other threads. What I suggest is... read up a bit to get some of the basic concepts and understanding, then just play the game and get experience. You'll learn more that way!