How? The only way to prevent the site or the postal service from potentially being used for sending CSAM is indiscriminate surveillance.

Do you also think the government should be reading everyone’s mail? Should they be scanning every device capable of storing data ever shipped?

Though they seem secure behind a paywall, swiping content creators’ explicit photos and videos from subscription-based platforms such as OnlyFans, Patreon, and Fansly is relatively easy. People can download third-party apps for the task, and if those don’t work, a few basic coding tutorials can teach them how to surpass anti-theft technology. These images and videos then proliferate across the internet, on niche forums, Reddit threads, Discord servers, and Telegram groups with tens of thousands of participants. Today, a growing legal consensus considers this activity to be sexual abuse.

I think you deliberately skipped this part.

Damn, I can’t believe I accidentally sexually abused Kate Winslet by pirating Titanic.

I think the risk of losing data naturally leads to people seeking out the most robust storage solution possible when 90% of those people would probably be better off with something simpler with less that can go wrong.

I can’t answer each bullet (and a couple are dependant on other things like drive speed, activity, and network throughput) but I’ve been using shucked external HDDs for over a decade and would recommend it. I used to use OpenMediaVault running in a VM on Proxmox and briefly tried TrueNAS, but I’ve since migrated all of my VMs to LXCs, so now I just have the drives mounted on the Proxmox host directly combined with mergerfs (not managed by Proxmox’s storage pools) and I pass it through to a Turnkey Linux file server LXC via bind mounts to share over SMB/NFS. Less overhead and LXCs can share CPU/memory dynamically while VMs can’t.

You should be able to replace that /mnt/external directory with no issues as long as the structure is the same within.