I know that we need 535 defense for heroics and 540 defense for raids but do we need a certain hit rating and expertise rating before we are able to be effective tanks?
To be an effective tank you need to stay alive and hold aggro on whatever you are tanking. Expertise and hit rating will help you hold aggro and you should shoot for the numbers already posted above. However, they are easier to obtain as your gear gets better. A low number in either area should not prevent you from tanking most anything.
I also wouldn't be suprised to have aggro issues if your just joining the tank game, since it's a little late in this cycle. You'll run across plenty of very well geared dps by now that may out-aggro you since your just starting out.
Originally Posted by Dravok
I also want to ask when and how often we should use our tanking cooldowns (IBF, UA, VB) and is there an addon that can flash a reminder that they are off cooldown?
Many bosses have a specific moment when you should have a cooldown ready to negate their high damage spells or attacks. It'll take a while to figure them all out but that's generally the use for all tanking cooldowns. For trash mobs or tank and spank bosses you can use them as you see fit. An addon would help with that. I use the tellmewhen mod if I want to see spells that are done cooling down and buffs or debuffs. There may be better ones.
I just want to make sure all the stats I have will keep me holding aggro. I would have taken up tanking a long time ago but I just get scared thinking Im gonna ruin it for the group. I need to get over that hump.