I think everyone else already went over why USB isn’t great, why mixing raid with zfs is outright terrible, but I guess I’ll add my $0.02 too.
If there is a single internal SSD, then mixing the OS & APPs on a single drive is an additional headache.
Cache is its own discussion on “why you likely don’t need it unless you can explain the type of cache & your specific use case; otherwise there is a good chance of additional problems”.
In short, this is likely a great little system to run some backups & docker, maybe a few light VMs… but not with TrueNAS as the OS. Nothing you posted is actively wrong… unless you add ZFS on-top
The worst problem with any of this is that there is a good chance it’ll initially function on TrueNAS. There is a solid chance it’ll find the drives, let you make a pool, maybe give some warnining you can ignore & initially look fine. It might even work great for weeks or months.
Then something stupid will happen & all data will be gone with little to no chance of recovery. I’ve personally seen examples of raid controllers, USB enclosures, port multipliers & various combinations of all three failing on the forums…