Lilyhearts wrote:
...can I heal people from both factions? My character is actually pretty independent and is searching for a Death Knight to accompany her on her travels throughout the Servers to help people in need of healing and protection.
Yes, but it's very difficult.
Healing people from your own faction is simple. Select injured person, trigger spell, voila.
Healing people from the opposite faction requires you to switch them to your faction briefly using Mind Control. That means you can only ever do this to opposing faction characters if they are flagged for PVP, since Mind Control is a hostile act.
Alone, you must cast Mind Control at the character. Once you have taken control, you may cast an instant healing spell on them such as Renew or Circle of Healing. Casting the heal will break your Mind Control, but since the spell is instant it will still affect your target.
If you have a like-minded partner, you can cast Mind Control on an opposing faction character and your partner can heal them, either by using spells, or if your partner is a Death Knight with no healing spells, simply by bandaging them. Your partner's spells and bandages won't break the Mind Control, so you can heal more effectively that way than you could alone, and you can finish up by breaking your Mind Control by casting an instant heal or a buff, such as your Power Word: Fortitude.
Keep in mind that anyone you could do this to has basically declared their preference to fight you by flagging, or by rolling on your PVP server, or by joining the battleground/arena. Not everyone will react kindly to you casting Mind Control at them--they may respond with hostility before you can get the spell or the heal off. Also, they may not be grateful.
Lilyhearts wrote:
Hmm...what's the strongest staff and magic a human priestess can possess?
That's a broader question than you suppose, and by the time you reach a level where you could find and use any of the game's current most powerful weapons, the new expansion will have been released and the bar raised. That said, the toughest raid boss currently in the game drops the Golden Staff of the Sin'Dorei, which any healing Priest would love to have.