Whats the upper limit on Task volume?

Recently not a student, I am moving all my stuff stuff back into my parents house and have a project to remember things that I need to move out in about 6 months. I wouldn’t hesitate to use omnifocus for this except that I could come up with other very very large projects in the future (i.e. templates like reading every section of every chapter of a text book) and want to know if omnifocus can handle these types of usecases… Are Databases of >5-10k tasks kosher in Omnifocus?

Modern databases can handle quite large volumes of data, but you may be unhappy with response times depending on the device you are using. But why would you want to do this? In the example you give of textbook reading, it is likely to be a colossal waste of time to set up such a detailed outline in advance, because each chapter has a different number of sections, et cetera. If you want to do something like a section a day, this is better handled wth a repeating action. If you want to get through a textbook in a fixed amount of time, a chapter schedule is usually sufficient (I am a college professor). If you are tracking a course syllabus, I recommend using it as frequently-reviewed reference material in order to track the course (and of course the instructor may make changes).