Linux Chromebooks are great! I have a Toshiba Chromebook 2 that runs gallium OS and it's been a nice little machine for several years now. It's getting a bit old so I'm considering replacing it at the end of the year. Here are a few things you should know before getting started.
1. Make sure you get a machine with a compatible processor. I believe only x86 intel CPUs will work.
2. You will likely need to flash in firmware and possibly remove a write-protection screw. Have a screwdriver that can manipulate little laptop screws.
3. Upgrading the SSD is STRONGLY recommended. Most Chromebooks come with 16GB ssds, grossly insufficient for a proper PC. You can get a 256GB ssd for as little as $40. Make sure it is the correct size for your machine. Suffice to say, be sure to get a machine with a removable ssd.
4. Do NOT install Gallium OS. Although my currant machine runs Gallium OS and most old websites will point you to it, it is an abandoned project (no updates in nearly 3 years). I'll probably install Debian with XFCE, but the anything distro with a lightweight desktop environment should be fine.
Here's a site that will walk you through the changing the firmware, it also has a list of comparable devices.https://mrchromebox.tech/#home