The NJO series did a lot to expound upon the ideas about the Force, I really enjoyed them towards the end. Out of all of them, I enjoyed Traitor the most. And with regards to killing Chewie, I think the cardinal rule that Lucas stated was: No killing Han, Leia, or Luke. Anyone else is fair game in the advancing of the storyline. Of course, that probably means no depicting their death. If a book is written right now 500 years after A New Hope, no one expects any of those three to still be alive. Unless they turn Luke to the Dark side and he rules over the galaxy with his iron fist.
The new Dark Nest trilogy got kinda draggy though.