FOr Defenseive Ratings as a Tank you need to have a 540 Rating to not be critted.
Your Gear is ok as is to be able to Tank low level 80 instances which should allow you to get better Tanking Gear as you go. Workon your Rep with the Argent Crusade to get their Helmet Arcanum. I am on Blade's Edge Server as a Pally Tank. Toon Name Thenis. You can check on my Gear there.
