I was able to confirm that there is no specific upper limit for Q1. However, we are not sure about Q2.
Is it a specification that volumes can be created and deleted using the API during the registration process in the Qtree DB? In other words, even if you create or delete a volume during the process of the light blue in the attached image, the API will run without waiting? The API never waited for us, but we'd like to know if this is the behavior we're expecting.