1. Highest +shadow damage or +dmg you can get
2. 76 spell hit rating
4. nothing else matters
If you intend to PvE raid (i.e. need to kill level 73 bosses), you need 76 spell hit rating. Get that first and then whore damage. Veiled Noble Topaz if you need hit. Once you have 76, nothing but Runed Living Rubies all the way. Ignore all socket colours unless the socket bonus is +dmg and it works out to the same or more than socketing with +9 dmg rubies.
Spell pen is not needed for PvE. It reduces the target's resistance against your spells. It's generally considered a useless stat.
Also, the higher your shadow damage the more mana you get back. The actual size of your pool doesn't matter, how much is coming in than is going out is more important.
I did most of SSC/TK with a 6.9k mana pool unbuffed. No issues. The only thing tho, is that as a gearing up spriest, its a given that you need to really abuse Mana potions and your shadowfiend. But if you can time your pot/fiend cds properly, you will never run oom. (i.e. pot early to top yourself off, not when you are low... etc etc)
You don't need to stack stam either. Just remember that you need at least 8k buffed to start SSC/TK.... some fights require more esp when you are learning. And in BT/MH, you need 10k buffed on certain bosses.
Since you are leveling, its not that impt now... just pimp out your dmg and you'll do just fine. Have fun smashing the dmg meters on 5 mans!