You have the theme:
"Thus, a custom staff must always be created around a single trait. For example, an elemental trait (air, earth, fire, or water), energy trait (acid, cold, electricity, fire, sonic, positive, negative, or force), alignment trait, the detection trait, the light trait, and so on. The staff and its spells must have the trait."
The example says "Lini, a 15th-level druid, wants to create a staff to interact with the plants she encounters. She chooses the plant trait to represent that theme."
That's the spells trait.
Then the staff trait:
"Choose a magical school for your staff from among the schools the spells on it have. Pick the one that best reflects the spells, usually the one most shared among them."
The example says:
"Lini selected mostly transmutation spells for her staff, so she chooses the transmutation trait."
So Lini's staff ends up with the Magical, Plant, and Transmutation traits. The spells trait is restrictive—every spell must have the Plant trait. The staff trait is not—she's selected mostly transmutation so chooses that trait but spells can be from any school.
Lastly, "You can optionally give your staff a trait for one magic tradition, instead of the magical trait, if the staff is fully steeped in that tradition and contains spells only from that tradition’s spell list."
So she could choose to give the staff the primal trait, replacing Magical with Primal. But that would restrict the staff to only Primal spells.
So 3 traits, although Magical is a default and there doesn't seem to be an option to select a tradition.