Inscription makes a truckload of gold, but the bonuses aren't great for pvp. I have herb/scribing on an alt (tauren) DK with On a Pale Horse so he can spend half an hour a week zooming around the river in uldum and making literally thousands of gold selling glyphs for 150G+ each.
It took me about a fortnight of BGs to get used to Sub at 85 honestly, it can be...interesting to deal with positional requirements. And getting used to shadowstep is hard even when you bind it you'll run through people a lot of lose your sense of direction. A few things to consider:
In BGs you will often open with garrote because you'll find people dismounted fairly often (already engaged in combat). In arena matches, the person you sap is often not the guy you'll be opening on. So you almost always have to cheap shot just to get your damage in cause they'll be mounted and running around. If you do garrote at some point, shiv straight after to apply crippling, it makes the positional requirement a breeze to deal with.
Speaking of which, poisons are MH wound/mind numbing, OH Crippling, thrown crippling for fan of snare. I almost exclusively use mind-numbing, it is amazing because chances are you'll be on a caster at some point in the match and that debuff is incredibly noticable. It also slows hunter cobra and steady shot by 30% and as a bonus helps make your kicks easier. Utterly overpowered in every way, and you should be abusing it.
I spec and glyph like this
. Yeah, it's super defensive but i pretty much only do 2v2 double dps. You should probably drop cheat death for 2/2nightstalker or 3/3 HaT and 2 more points in assassination for 3/3 puncturing wounds.
Always hemo once after opening to get the +10% damage bonus from bleeds (not required with a garrots opener obviously). How you open depends on the situation. If you're in a really really good one (kill target in a bad position far from a pillar, at least one person cced) and you think you can get a kill, you can open with garrote > shiv and a 5pt kidney shot then drop smokebomb (or 5pt evis if you opened with cheap shot). Otherwise get recup up and running asap.
Always always get crippling up, not just to peel off your hunter. If you catch someone in the middle of nagrand with a 70% snare and your hunter on them they are in seriously deep ****.