1.
Take your pick, level as Mutilate with daggers, or Combat with whatever weapon happens to be the highest dps, out of all the weapons you have.

Mutilate spec, will be Mutilate as your DPS move.
Combat spec, you'll spam Sinister Strike.

2.
Don't bother with Ambush/Backstab.
Easier to just Cheap Shot x1, Mutilate with everyone else.
Then you don't worry about facing.

3 & 4.
For PvE, you want 8.50% hit, 26 Expertise (not sure the ratings).
I believe you only need 4% for PvP, not sure on the Expertise there either.
Armor Penetration is a good stat.
A lot of rogues gear PvE for PvP, and in battlegrounds this is probably decent for killing.
The stamina/resilience gear, will be better once you have a bunch of it.

5.
With a Mutilate/Preparation spec (50/0/21), you'll apply Crippling Poison for free, by using Instant, Wound or Mind Numbing.
I would go Wound/Mind Numbing on one or two, and Wound/Deadly on the rest.

6.
In AV, as a solo rogue, I use stealth to sneak into the last base, and cap the towers.
In WSG, you have Sprint x2 and the Speed Boots, plus stealth to get into position; Blind, Cloak, Dismantle, Evasion etc.
In AB or EotS you can "Distract", to frequently send people off of cliffs to their deaths.
Any time you decide to cause chaos in the middle, you will.

7.
I use Cooldown Count and Dot Timer for cooldowns/timers.
Deadly Boss Mods, is good for battleground related timers.
Have not really gone with a bunch of rogue specific addons.

8.
My rogue is primarily PvE focused; I've gone with Inscription + Jewelcrafting.
Inscription was a largest profession boost over not having that profession, for a rogue. Plus did not need to level Hodir on this toon.
Jewelcrafting both as a decent money maker and for the Dragon Eye gems.