How to build a backup solution from scratch

Putting together a backup solution can be a pretty daunting task when trying to consider all aspects at once. You mention that all decisions are up to you including policy and equipment and you are wondering about a standard.

Unfortunately, when it comes to backup policies, there are no "best practices" or standards; every organization is different and has specific recovery requirements (financial or legal).

My first piece of advice would be to start with the business requirements; this will pretty much dictate whatever else you have to do. Backup data retention will dictate storage capacity; Recovery Time Objectives (RTO) and Maximum Tolerable Outage (MTO) will dictate storage devices and network performance.

Backing up, and mostly, restoring a terabyte of file server data over a geographically dispersed environment to a central location can be challenging if not impossible. Unless your organization has access to fiber connectivity across sites or unlimited network bandwidth, other options might be better suited. For example, a combination of remote replication to disk to a central location and a backup of that replicated data might be a better option in your case.