Cut your first log where the base turns into a normal trunk without all the gnarly stuff.
On the tree in my pictures I had the same type of base but good straight wood above the stump. After I got all my straight logs loaded I went back and cut the gnarly part off the stump.
I made sure I could cut a billet length section of the gnarly base or about 42". I later split the best parts of this base into billets, trashed the unusable stuff.