Do you want to enable transcoding? If so, do you want to provide multiple resolutions per video? Try this out with a few videos and you will get an idea of how much extra space is required per video and estimate a multiplication factor for future space allocation.
Enable <a target="_blank" rel="noopener noreferrer" href="https://docs.joinpeertube.org/admin/configuration#live-streaming">live streaming</a> for your instance
Enable or disable signup, <a target="_blank" rel="noopener noreferrer" href="https://docs.joinpeertube.org/admin/managing-users#registration-approval">approve manually new users</a> or set upload limits