https://grafana.com/grafana/dashboards/893-main/
this would allow you to log the network usage per docker container, and you can then use grafana's integration function to get total data sent/recieved over a period of time.
this was just using a quick google search
I use my fortigate router as it logs everything natively. Logs DNS request, outbound traffic, internal lan local traffic, and so much more
yes, i am over 100TB and backup everything on two sets of external disk arrays. one is at my house only powered when i perform my monthly backup and the other is at the in-laws house. i swap the two sets every 3 months
here are the enclosures i use
https://www.amazon.com/gp/product/B07MD2LNYX. between all my backups i have 4x of these enclosures and 32x drives
backup 1
--> 8 bay USB disk enclosure #1: filled with various old disks i had that are between 4TB and 10TB each. the total USABLE space is 71TB
--> 8 bay USB disk enclosure #2: filled with various old disks i had that are between 4TB and 10TB each. the total USABLE space is 68TB
Backup 2
Exact duplicate of backup #1.
i have windows stable bit drive pool to pool all of the drives in each enclosure. i also use bitlocker to encrypt the disks when not in use.
Synology