In my opinion the setup is pretty easy. All you have todo is go to
MrChromebox.tech website
search for a device that uses "screw or jumper " as WP Method (Write Protection Method for the BIOS Chip) Why is this important ? From what i know, the CR50 Chromebooks use a Security Chip from Google some mixture of TPM and Management Engine. So i try to avoid these.
And lookout for the “UEFI Firmware (Full Rom)” option. This means the flashing coreboot process turns your chromebook completly into a coreboot Laptop (Chrome OS will not work after the process)
When you have some models that fit your needs, head over to the Gallium OS (a xubuntu version that is tweaked for chromebooks ) wiki and look up if your laptop is well supportet it is kind of gambling because it depends on some things like your kernel for example. But i would recommend some research on reddit etc to find infos about your chromebook model.
Since this model uses coreboot with tianocore as payload, it is pretty straight forward.
Open Case, pull out the hardware protection screw
Boot Chromebook in recovery mode
Enable developer option
Boot up into guest mode
Open Shell
wget a script from Mr Chromebox techs website
Follow the script and use “complete alternative firmware”
Wait for it to finish
Reboot and you will see the coreboot rabbit
Press ESC
and boot up the Qubes OS installer
Lowering the Memory/CPU option in Qubes Manager for your AppVMs is good idea.
Testet with disposable sys-net/sys-usb and whonix.
Again its best for surfing, reading ebooks, some youtube or writting. I thought thats a good option for journalists. Since this Chromebook C740 is pretty lightweight, small and has a relatively long battery life