Few questions regarding LotR

My first ever post (BTW, why hasn't the name Ecthelion already been taken, or has it?)!
Regarding your post, Dealing with the Erkenbrand question first.
Erkenbrand was the general of Rohan's army. He and Theodred(Theoden's son) led the majority of Rohan's armed forces against Saruman's forces at the battle of the ford of Isen. Rohan lost this battle, Theodred was slain and the remaining forces were routed/scattered. When Gandalf left Theoden before the battle of Helm's Deep he had two tasks to perform: 1. Contact Treebeard and request the Huorns needed to ring the battle field. 2. Gather the scattered men from the battle of the ford and contact Erkenbrand. This isn't really given alot of time in the book but is in the appendixes.
As for your first question, others are bound to know the answer better than I. My responce none the less. At the time of LoTR there are essentially four places in middle-earth where elves dwell. They are Lindon(Grey Havens and west), Rivendell, Lothlorien and northern Mirkwood.
Thranduil was king of the N.Mirkwood elves. What differentiates them from the others is that they are Sindar(grey elves) and as such never made the great journey to Aman. For want of a better word they could be considered less 'civilizied' than other elves (thats not to say they are savages, but they never saw the light of the trees or the Valar).
Lothlorien elves were also Sindar(I think, help please?) but Galadriel wasn't (since she was if the Noldor, who all went to Aman... and came back).
Most of the elves west of the Misty Mountains were presumebly of Noldor stock. In writng this, I am suddenly struck by the fact that I can't think of anything that distinquishes the settlements of the elves, only which seperates them racially (Noldor from Teleri etc). Sorry.