I’m replacing previous RPI3 based INDI-server with new RPI4 which is booting from uSD-card but running the OS itself (Ubuntu 22.x) from SSD. Yes, you can run Ubuntu (or FreeBSD etc…) on Raspberry with USB, SSD or M.2 disk attached. VirtualBox is a good development environment and simulation platform. The last image here shows my recipe for building INDI from source code without GSC-catalogs which are needed for off-line plate solving.