Are you seeing high IOWait? How did you determine that it's an IO issue?

I can download/write + stream to multiple users off a HDD that's MUCH slower than your SSD without any issues, so I suspect something else is going on.

Will a HDD work for my purposes?

HDDs are much slower than an SSD, like more than 30,000x slower on IOPS.

3-2-1 is the minimum I follow for anything important.

1 copy is the working data, 1 copy is a full system image stored on a NAS with incremental backups done nightly with Veeam, and 1 copy is on Backblaze B2 with incremental backups done nightly with Restic,