This is kind of an obvious comment, but before doing something like
this you should figure out what kind of outgoing software support
there would be. If there isn't any, then the students are unlikely to
use these computers, and will use something they find easier. Unless
they are already very adept with Unix-like systems in general, and
Linux-based systems in particular, which seems unlikely.
Yes. Makes sense.
And from a more bottom line perspective, if there isn't anyone to
maintain the machines, they will eventually stop working. Even Debian
can't completely run by itself, and does require some maintenance.
True.
They have a computer teacher. May be we can get him started to to mainten the system. Or teach him how to seek help.
Another option is we begin with only 2 machines instead of 20. And once a month or two revive them if broken.