Until you really understand EH and avoidance needs for the content you are doing, put +12 stam star of elunes in every gem slot regardless of gem color. The only exception to this rule is if you have a gemming bonus that will give you a similar stam value with more defensive stats. For example, an item with 1 red and 2 blue slots and a +6 stam gem bonus would be best gemed with 2 star of elunes in the blue slots and the +4 dodge/+6 stam gem in the red slot.
Forget hit entirely until you have enough EH and avoidance for at least kara level content and your expertise is over the soft cap. At that point look to badge gear to get your your hit up to the soft caps (though honestly it will probably be their naturally due to gear). Don't gem or enchant for them, get them off of gear upgrades.
For enchants, you will look for stam enchants where possible, and avoidance enchants where not.
As for unbuffed HP, for going into heroic content you're going to want to be over 12k hp if you're going with a good group with a healer who knows you and understand they're going to have to work hard. The less familiar with the healer you are, the more unbuffed hp you'll need. 12k HP is not hard to achieve.
Expertise is one of your most important offensives stats, but ignore it until you are into t4/5 content. Once you've got 3-4 badge pieces, you'll need to start worrying about choosing gear based on expertise impact and balance that with your EH and avoidance needs. But before then, stam, stam and more stam.
Edited, Aug 1st 2008 9:59am by kingpatzer