I have a 512GB internal and use it for apps and user accounts primarily. A few apps installed a lot of data that is almost never used, and by using DaisyDisk to find that data (~230GB), I have moved it to an external drive, and replaced the folders with symlinks. Simple, one time procedure, basically. This way, my internal is mostly around 50% free space or more.
I have two 4TB and one 2TB ssd in 40Gbps external enclosures that are connected all the time, with both photos/videos/sample libraries/projects etc., and backups - so that if any drive should fail, I can replace it and restore its contents quickly.
I also have 3x2TB 2.5" SATA ssds with clones of everything, stored at my neighbour's house and updated every other week, in case of total disaster.
Update:
I've moved stuff around a bit, and here's my new storage setup:
Internal drive: as before.
Primary external drive: 4TB SSD Thunderbolt4 (40gbps):
as before, w/my three main volumes:
Neptun, Jupiter, and Venus.
~1800GB free space.
Secondary external drive: 4TB SSD Thunderbolt4 (40gbps):
Install macOS, bootable installer (HFS+ partition).
CCC MAX, backup with APFS snapshots.
Saturn. For things that don't need backup, sample-archives I can redownload if needed, short-term storage etc.
~2800GB free space.
Third external drive: 4TB HDD USB-A, USB 3.2 (new):
CCC backups of MAX, Neptun, Jupiter, and Venus (Because of the HFS+ format, each in their own folder, and not on volumes. CCC Safetynet kept for 50 days.)
~1600GB free space.
This way, I've freed up two ports, one 4TB and two 2TB NVMe and a few NVMe enclosures. The HHD cost me ~$200usd, and selling the NVMes and enclosures will earn me a good profit. Plus, it's pretty slick and streamlined this way.
My next door secondary backup is the same as before.
BTW, I was pleasantly surprised by the performance of the new HDD. I got about 220MB/s, which is far better than the HDs in my old mac pro, they were around 70MB/s.