Acer e5-573 Intel Celeron 2957U 1.40 GHz 2 Cores 2 Threads, 12 GB Ram.
The 2957U Processor seems to me very weak for LZX Compression, For Ram boot it should work as all is on Ram, but even from Ram it will feel slow, I would use Compact 4K Compression (or Express 4K on wimlib terminology) for file booting on this CPU.
Asrock Q1900-itx Intel Celeron® J1900 2 - 2.42 GHz 4 Cores 4 Threads, 8 GB Ram.
The J1900 Processor is not so weak as the other, but it isn't a powerful Processor too.
About the USB devices:
Sandisk cruzer blade 16GB usb 2.0 >>> You may boot some WinPEs from it as they load to Ram, but USB 2.0 is too slow for file boot a VHD fine. Don't use it for this task. I booted once a uncompressed XP x86 VHD from a USB 2.0 stick and it was so slow it was unusable, but from a USD 2.0 HDD it booted fine.
The other 2 are USB 3.1 devices, they look fine, and they should work fine too.
So the Asrock Q1900-itx (Intel Celeron® J1900, 2 - 2.4 GHz 2 Cores 4 Threads, 8 GB Ram), should be capable to file boot a 10x64 LZX VHD from a USB 3.0 device, maybe a few slow (depending on actual USB speed) but it should be definitively capable to do it.
Better check following settings in UEFI Bios/Firmware:
Is Fast Boot disabled on UEFI firmware?
Please verify and if it isn't disabled, disable it.
From your MB Asrock Q1900-itx Manual, pag. 49:
Fast Boot minimizes your computer's boot time. In fast mode you may not boot
from an USB storage device. Ultra Fast mode is only supported by Windows 8 and
the VBIOS must support UEFI GOP if you are using an external graphics card.
Please notice that Ultra Fast mode will boot so fast that the only way to enter this
UEFI Setup Utility is to Clear CMOS or run the Restart to UEFI utility in Windows.
About USB, on the manual on pag. 43, it says this
Enable or disable all the USB ports.
USB 3.0 Controller
Enable or disable all the USB 3.0 ports.
Legacy USB Support
Enable or disable Legacy OS Support for USB 2.0 devices. If you encounter USB compatibility issues it is recommended to disable legacy USB support.
Select UEFI Setup Only to support USB devices under the UEFI setup and Windows/Linux operating systems only.
I would try first all 3 enabled, and try file booting from your USB 3.1 device.
If previous setting don't work, then I would try selecting UEFI Setup Only on Legacy USB Support option, and try againg file booting from your USB 3.1 device.
When selecting UEFI Setup Only, if you have a USB keyboard, maybe you can't use it, if booting from grub4dos, better keep the filedisk booting as default option on menu.lst, or don't use grub4dos in this case, and boot from Windows boot manager directly.