Yes, Northern Stronghold essences are the best available and you can enough of those essences once you finish all North Mirkwood quests (Newest region)
Regarding the gear, I would recommend getting those teal pieces without set bonus from Dor Amarth npc's, they are pretty cheap. You should be aiming for at least 150k finesse and 90k unbuffed morale right now, and once you get the t2c raid gear try to up your finesse to a bit over 200k.
With the teal pieces alone, Your mits will be somewhere close to t2c cap for Light armour, you can grind some virtues to push your mits further. So basically just use all of your essence slots for Vitality and Finesse, mostly Vit.
Read the stat bonuses on jeweleries and off hands and decide which one benefits your build more. For example just because a piece has +Agility stat instead of +Will, doesn't mean its useless for Yellow LM, as some of the agi pieces has decent finesse bonus.
Good luck on gearing
