Since you're comfortable with linux, you really don't need a tutorial. Just buy a cheap minipc or maybe a raspberry if you fancy it, install the distribution of your choice or something more complete like OMV7, plug your enclosure and you're done

That could work. The only thing I have noticed with my laptop+ enclosure based setup is that the disks go to "sleep", probably due to power management, so if it has been a while since I accessed the contents, I need to click on the mount point in the explorer window for the disks to start spinning and the files to be available again. I don't want to deal with that so I was thinking that a box with slots for multiple internal disks will not have such issues. I can try to tinker with USB power settings but that could be a time sink/brittle solution.