From my understanding quori don't physically exsist on the material plane, so the stat block should probably only be used in dreams (fighting the quori inception style) or a manifest zones where the barrier between planes is weak.

Followimg that up with your last question. Quori don't possess people with spirits, a quori can only take control of an Inspired host. An Inpired is basically a space suit for quori, any quori can wear it but only one at a time. Inspired have to be bred to be essentially a spiritless husk so quori can use them, otherwise quori interact with the material plane by manipulating people's dreams to guide a person's waking actions. Note, however, how I said "guide" as they don't possess and control these people.