Every time you are about to design a tape rotation scheme for a backup policy/plan to be created, you ought to come from the following arguments:
full size of the data to protect
approximate size of the daily changes of data
approximate size of the weekly changes of data
requirements for the backup scheme (frequency, performance and duration of backup operations)
requirements for keeping backups (minimal/maximal period of backup keeping; need to store tape cartridges off-site)
capability of the tape library (number of drives, loaders, slots and available tapes; capacity of tapes)
requirements for performing data recovery (maximal duration)
You need to analyze every argument that is relevant for your case and select the main criteria for the choice. Then choose a backup scheme and specify the tape options.
Note, that any backup scheme in combination with different tape options will have quite different results for efficient use of both tapes and devices.