The only difference between a PvE and PvP server is that you're a free kill in any contested zone, which is everywhere except Westfall, The Barrens and the starting areas. Not sure if there are other areas, but that's pretty much the main areas.
Leveling on a PvP server, you'll get intimate with paranoia and looking over your shoulder constantly. You'll also invent a few new curse words. But it can be loads of fun once you get to return the favor.
Since you'll be leveling with a Priest, I suggest you go Feral for maximum DPS and survivability. You can pretty much do anything together if you go Feral and he/she goes Shadow. Being Restoration with a Shadow partner is pretty much overkill in the healing area. Plus, you rarely need two healers for instances. Going Balance is an option, but having two casters also creates some issues, not to mention it's not very efficient downtime wise.
If you go Feral, you'll rip through the mobs like a hot dagger through a Gnome spleen. Seriously. You'll be game over and the credits will roll before you know of it. The Priest, with a Shadow talent built, can deliver both damage and healing at the same time (Improved Vampiric Embrace = win) and your Druid with a Feral talent build can do massive damage in Cat form for those regular mobs that don't pose much of a problem as it is. Or you can duo elite mobs with ease if you go into Bear form and tank them while the Priest does damage.
Vampiric Embrace from the Priest's Shadow talent tree returns a percentage of the shadow damage the Priest does as health to everyone in the same party as the Priest. Since Shadow Priests pretty much only use shadow damage to harm their enemies, it's quite a bit. I believe the total health returned (with Improved Vampiric Embrace) is 25% of the shadow damage done. So if the Priest crits for, say, 500 damage with Mind Blast, that's 125 health returned. The Druid also gets such a nice talent, however, it works in a different way. Improved Leader of the Pack is a Feral talent which returns 4% of your total health when you deliver a critical physical hit (no magic hits, unfortunately). 4% doesn't sound like much, but with Nurturing Instinct (also Feral talent) and 2,500 health in Cat form, that's 120 health returned on each critical hit (max once every six seconds). And in Cat form you crit a lot. A lot.
So the Priest will be healing both you and him-/herself through dealing damage and you'll be healing yourself through dealing critical hits. This means you'll almost never run low on health, making it very mana efficient since the Priest won't have to drop Shadowform to heal and you don't have to shift form to heal either.
It also means that you are able to duo very tough mobs since your armor and stamina will be skyhigh in Bear form, effectively making you a brick of fur and with various taunting abilities, the Priest doesn't have to worry about pulling aggro.
A Druid and Priest combo is pretty much god mode in this game, I think. Especially since you also have the ability to heal a bit. Not to mention you can use the spell Innervate to return the Priest's mana. Hell, it's like a dream team now that I think it over. Probably the most efficient combo there is.
Damn.
Can I join you guys?
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Please "talk up" if your comprehension white-shifts. I will use simple-happy language-words to help you understand.