Others have reported success, and it should work, although I have not tested all of these distributions personally.
@FranklyFlawless summarized the Wi-Fi and Bluetooth caveats very well. You can order the Mini v2 without a Wi-Fi card if you intend to install your own AR9462 (and will not use Bluetooth as you mentioned).
PureBoot and Heads do not work with Guix currently (Guixsd vs Heads - How to make it work together? · Issue #753 · linuxboot/heads · GitHub). You can switch to coreboot/SeaBIOS if you want to use Guix.
Yes, all devices ship with PureBoot, which is our distribution of coreboot with Heads. You can switch between Basic and normal mode at any time (non-Basic mode requires a Librem Key). You can also switch between PureBoot and coreboot/SeaBIOS using our utility script.
Yes. PureBoot (or coreboot/SeaBIOS) are flashed in the SPI flash chip shown in that photo. If you have an SPI flash programmer (not expensive), you can reflash externally.