Shoulder first since his current shoulder is already offset. Then likely head for the two piece leaving legs and gloves for last since either could drop in VoA if you get lucky. Chest you would skip for the BoE chest, Ikfirus's Sack of Wonder (Gunship 25 or on the AH for more money than you can probably afford). Under no circumstances should any druid spend emblems on Saronite before getting set pieces. All three specs would priorize set pieces higher than off set.
Threat is more spec and proper technique (granted you are greatly limited by the effectiveness of your weapon as felhoof pointed out). You should never have to gem or enchant for threat, doing so typically means you are doing something wrong.
There are several alternative enchants that would be better for you (yield more effective health). 225 armor on cloak is better than 22 agility. 18 stamina armor kit on gloves is better than 15 expertise (since you are already over the soft cap and ICC bosses aren't parry hastable anyway). Chest is fine at 10 all stats, though if you're purely tanking another 18 stamina armor kit or even the 275 health enchant would likely be better for a pure tank. You shouldn't use a pure red cut either to meet your meta requirement, instead use a Shifting Dreadstone (10 agility, 15 stamina).
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.