Hi Eric,
Why do you need 4TB of local storage? I'm doing as much as I can to go the other way now - keeping as much as possible on my Synology NAS so I can access it from any device. That may be your constraint.
We have like a half a dozen Synologies in various offices in different sizes. None of them would meet Ken's "must be portable" requirement. <g> The other issue with Synologies is that in terms of data transfer it's hard to exceed 100 MB/second and the network adds extra latency, as does the SMB protocol. My external SSD connected to USB-C maintains 240 MB/sec and the internal one is a lot faster than that.
We tried TimeMachine backups on the Synology and storing our VMs there, but it was just too slow and buggy. We now use SSDs for TimeMachine and a lot of problems have disappeared.
I've 2 TB of storage, but constantly get error messages because I run out of disk space. I've moved rarely used VMs to an external disk, even though I don't like that. I guess videos need a similar amount of storage.