to 1) When you gear gets better in Karazhan, you'll often "downgrade" your gear, losing some HP Health and getting very near 490 Defense. If you have the HP/Armor du survive the battle, yes aggro gear will help you a great deal.
But for now, aim more for HP/Armor and Avoidance (which is King with the Prince).
to 2) I'm not 100% sure, but i guess it's the same for DW. About 200 Hit Rating. 25% Crit Chance and 1500 AP is very good for the start. You can also try just 136 hitrating (about 5% hit) then you specials like devastate wont miss anymore, but your rage generation could suck then because of the missing white hits.