How many characters are there in A Dog's Purpose?

There are several characters in the novel, and the main protagonist is the dog who is first named Toby and is reincarnated as Fella, Ellie, Bailey, Bear, and Buddy.
The dog seems to instantly love some of its owners, as is the case with Ethan Montgomery—a young boy who names the dog Bailey (and later Buddy) and loves him dearly. Through Ethan we meet his love interest Hannah and his former friend Todd.
Before that, the dog's owner was Senora (and Bobby and Carlos) who had way too many dogs and named him Toby. Here we meet Toby's dog family which consists of Mother, Sister, Fast, and Hungry.
Then we have Jacob—a depressed police officer who never got over his wife's death and ends up getting shot. He names the dog Ellie, and the hardworking and kind officer Maya is the one who takes care of Ellie after Jacob's death. Ellie becomes a part of the K-9 unit and meets four other dogs: Top Dog, Spike, Cammie, and Gypsy.
There's also Wendi, a lazy woman who doesn't really take good care of the dog which she names Bear. Wendi gives the dog to her parents, Lisa and Victor, who abandon Bear in the woods.