Hi @kevinwtbolger,
NFS v4 should work just fine. If you're configuring RSP with project sharing, you'll need to configure ACLs, which work differently in v3 vs v4. To be clear -- either should work, but configuration process is different by version.
For RStudio Package Manager, an S3 bucket can be used as a backend storage.
For RStudio Server Pro and RStudio Connect, the external storage volume must actually be mounted into the filesystem. You can technically mount an S3 bucket with certain external system libraries, but we do not recommend doing so for latency reasons.
Hope that's helpful!