I have always created multiples pools pre drive configuration for example.
I have a 25day server that I use for TrueNAS to present iSCSI targets and NFS targets.
What I have always done was create say,
Virtual Machine - RAIDZ2 (Driveslot 1-6) with 2TB SSD Each
Critical Machine - RAIDZ2 (Driveslot 7-12) with 4TB SSD Each
and so on. Is this the best way for performance since each drive is different size and etc?
Short answer is yes because mixing drives that have different performance profiles is not recommended.
Longer answer is here
I have also read from (I think) an IX Systems blog, that your vdevs are best set up with 8 drives maximum, you can use a stripe to combine these into larger storage and bring back some spindle speed. Not sure if it still applies, and certainly may not apply to Scale, but something I’ve done since learning about this.