Sizing repositories requires consideration of two primary factors: space and I/O performance.
While it is quite easy to build storage with enough space to store backups, doing so without consideration to I/O requirements will potentially lead to a solution that fails to perform up to expectations and limits your use of advanced recovery options. Veeam Backup & Replication stores backups as standard files, which provides for a wide range of possible storage solutions. Veeam supports writing backups to any file system supported by Windows and Linux, as well as directly on NAS storage devices using the SMB/CIFS protocol.
The recommended CPU and RAM for a repository is 1 vCPU/Core and 4GB of RAM plus 2GB RAM for each concurrent task.