Solutions
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Pear's post in Classicube Server on Raspberry Pi was marked as the answerFor the client: just go to the download page and click on the Raspberry Pi tab, download the correct architecture, and follow the instructions.
For MCGalaxy, get Mono (sudo apt install mono-complete on a Debian based distro, can't remember the rest) and get a copy of MCGalaxy here and then run mono MCGalaxyCLI.exe in the Terminal.