Where do you think the members of the fellowship were during "The Hobbit"?

[Lord of Angmar]

If Bilbo didn't see him then, when did they became so close friends as wee might assume from FotR's Many meetings(?) chapter.

Well, remember, Bilbo had been gone from the Shire for 17 years when the Many Meetings chapter in Rivendell took place. So he could have easily become friends with Aragorn in that time.

I do not think that Thranduil allowed Legolas to partake in the Battle of Five Armies. I seem to remember Tolkien writing specifically that he did not. Besides, Legolas never mentions it in any of the LotR books.