[Tuor of Gondolin]

It's interesting that both Northern Mirkwood and Lorien
were established as entities by Sindar kings ruling over
woodelves, with Lorien later led by Noldor. The nature of
most of the peoples in both realms could explain their
reclusiveness, with the additional reason in Mirkwood of
Thranduil (and before him Oropher?) retreating from
the mountains of central Mirkwood to the northeast.

It seems probable that the giant spiders were the offspring of
either Ungoliant or Shelob, but which? Since I believe
Ungoliant traveled to at least the area of Mordor it
seems possible she visited Mirkwood on the way.

Could there have been some sort of epic battle between
Ungoliant's offspring and ents in Fangorn?

Bilbo is seen at his most heroic, and I think Likeable, here,
displaying loyalty, courage, and intelligence. That'll teach
them dwarves to question the judgement of a wiuzard!