The Skull Canyon i7 NUC will probably work, but for example, I need to iterate with someone who has one to find the right driver options in Linux to enable the thunderbolt ports, and then support hot plugged auto-mounting of thunderbolt drives.
Onboard storage is not supported in Roon OS… maybe a future revision. This mostly has to do with the recovery mechanism in case you brick your device.
Updates to Roon OS work just like Roon, inline and very streamlined. It is not a very DIY solution in the software space… just allows for hardware DIY.