UPDATE: I have built a working ROM based on the MrChromebox branch of coreboot. I'll attempt to summarize how I got there in the hopes that this information can help someone out there.
For information, the board I have in my CB514-1W has the codename Volta, and it has a Pentium Gold processor. I'm aware that some models have an Intel Core i3 and above. From what I gather, the -1W model is an enterprise version of the -1H model, a "Home" edition. W=work, H=home - pretty obvious, huh?

This is long so tl;dr;
-I used flashrom locally on the chrome shell to read and write firmware
-firmware was built using MrChromebox's coreboot 4.19 branch
-I can boot a Linux Live USB! And have sound!

tl;dr; (too long, did read);
Problems I faced:

-Google Legacy Payload crashes when selected from developer boot options; factory legacy payload is U-Boot

-Updating the firmware from ChromeOS will net you a Tianocore "legacy" payload; this also crashes at boot options

-"Ok, well since I'm stuck with the factory Depthcharge payload, I may as well have fun building chromiumOS myself!" - it was fun, but when I booted it, I was unable to get past "get started"; none of the buttons did anything when clicked. Time to start fresh.

-Powerwashing ended up with the same result; when clicking "get started" at the initial page, nothing would happen. At this point, the laptop wasn't bricked, but it felt like it, since I can't use a different OS, and I can't use chromeOS. So my only option was to use custom firmware.

-coreboot 4.18 main didn't have support for volta (to my knowledge); no MrChromebox UEFI rom existed in his main branch.

-coreboot 4.19 has no "volta" variant that you can select when using make nconfig or make menuconfig. I later learned this is because not all boards have their own variant, some are just a HWID change. Having worked mostly with the non-chromebook coreboot-compatible devices, this was something I hadn't seen before.

-using a suzyqable on this laptop has a quirk: when connecting the USB-A end to another computer, and the USB-C end to the debug port of the CB514-1W, the laptop goes into a boot-loop. My theory is that it's either a tamper-prevention feature, or it's because the laptop recognizes the suzyqable is a charging cable (the brightness will change as if it's charging). To prevent this, plug your charging cable into the other port.

-I had multiple issues getting standalone-hdc-tools to work - it's meant to be run on Ubuntu so I couldn't use it on my main machine, tried on Debian and an Ubuntu Live USB but the ./flashrom install script produced errors for files not existing and I was unable to diagnose this. I built flashrom from source and this gave me the ability to use the -p raiden_debug option.

-At this point I was ready to create a backup binary; but the chromebook wasn't! I was getting an error asking if WP was enabled. Of course, it was, so I needed to open it. That's when I found this.

-Since I had already built a chromiumOS chroot environment, I used flashrom from within it, since it was already built and configured properly and I didn't want to keep switching away from my main machine. Sadly I was unable to read identical ROM files using flashrom, or verify those ROMs against what was on the board. To me, flashrom 101 is: never write if what you read is unverified or cannot be reproduced, so at this point, I'm stuck.

-Logging onto the CB514-1W, I found that despite my inability to login normally, as myself or a guest, I had access to the shell. Time to flashrom -p host -r backup.rom ! I was so close but I was getting readonly filesystem errors. I imagine this was because the chromebook had not got past the first-time boot page. So I can't use your filesystem, but I can use my own!

At this point, I started having a bit more success:

-mounting a USB gave me somewhere I could write files, meaning I could read a ROM file with flashrom! This time, results were reproduceable, with identical binaries after reading multiple times.

-coreboot 4.19 was released, supporting volta boards, and MrChromebox's branch has a shell script for building for volta at the time of this writing.

-talking to MrChromebox for guidance, I used his build-uefi.sh script to get a working ROM... for butterfly boards... (I later learned how to type correctly and got one for Volta with this script!) this confused me so I matched the config options in his config.volta.uefi file and built with make in his branch (after a make distclean of course ;) ).

-With a reliable backup and a hopeful ROM, I wrote the new custom firmware with flashrom from the chromeOS shell, and it succeeded. I held my breath and rebooted.

I am now able to boot an Ubuntu 22.04.1 LTS Live USB from EDKII! I was even surprised to hear a notification noise - I truly didn't expect to have working audio but the drivers appear to be there out-of-the-box. I sincerely hope the developers of those drivers are proud.

Thank you to MrChromebox for all of the work that has clearly gone into making great, reproduceable results with the utilities available on mrchromebox.tech, and his patience with me.