If you're using traditional license, you'll need the 'Advanced Backup to Disk' (per TB) based on your source data.
If you're on capacity license, just get the amount of TB equal to your source data to backup.
On the StoreOnce by default it comes with deduplication. There are only 2 licenses available - replication or Catalyst. Read up their quickspecs on the differences.
I recommend the Catalyst license so you can do server or source-side deduplication with DP.