Question about Shaman King Manga

I recently started reading the volumes of Shaman King from the library, hiring out the first 20 volumes yesterday. However, I've heard that the manga ended abruptly and without a conclusion.

I've also read that there is a Kanzenban release that contains extra chapters not included in the volumes, so do those chapters finish the manga and should I find them after I finish reading the volumes?

Yes and yes. As far as I know.

My own colelction is kind of on stasis, as my local Barnes and Noble insists on having about 7 mismatched volumes that never change.