Now that the system seems to be pretty stable after all if you stay within the power budget, I decided on this configuration for mine:
- 1x Transcend TS120GMTS820S in slot 4 for the OS
- 5x Crucial CT1000P3SSD8 in a RAIDZ1 for the pool
- WiFi & Bluetooth removed
- eMMC erased and disabled in the BIOS
- LACP uplink and everything on VLANs on top of that
- TN CORE and potentially zVault
Only thing - if you check the download site for the BIOS updates there are two files that hint at a 16 GB RAM version. Gnaaa …
But jails are low overhead, so … 
And to close a PSA:
For automatic power on after power loss in the BIOS setup navigate to:
Chipset > PCH-IO Configuration > State After G3 - change to [S0 state]
PSA2:
The two Ethernet interfaces are each in their own IOMMU group. So you could pass one to a VM regardless of the host OS (Linux/FreeBSD), and use that as e.g. WAN for a dedicated firewall VM.
Take care,
Patrick