[Eldar14]

It seems to me that the best choice would be to use Melkor/Morgoth and Feanor as the two main characters. While Feanor may not be in the whole book, his actions, primarily the creation of the Silmarils and the Oath, are some of the main driving forces for a good majority of the plotline. Also, these are two very good characters in that a good amount of the book is about strife between Morgoth and Feanor/his sons.

Alternatively, since the Silmarils, even though they are an object not a character, are in many ways more important than the primary characters in many novels. So, if possible, it could make sense to choose Morgoth and The Silmarils as the two main 'focuses,' instead of characters.

As far as secondary characters goes, the problem isn't finding at least five, but deciding which of the numerous characters qualify. Also, it may be possible to group sets of secondary characters so that more of the characters can get their due recognition.