I could lend a hand, but be aware I'm prone to procrastination.
If there's any advice I'm able to give, it's to read a lot. That's the surefire way to figure out what works and what doesn't work. From what it sounds like, I think you could def stand to gain from reading the Hobbit and the Silmarillion by Tolkien, then see how all of that backstory found its way (or didn't) into LOTR.
what age group is this aimed at? is it like young adult fiction or more along the lines of fantasy for all ages? @
Totoro might be a good mind to leverage as well, I think he's more familiar with this type of genre than I am.