Advice about how to use Kirby best as quality management system

The CMS Questions
2

You can use roles to restrict access to the page. I think what you want is essentially described in this post., tweak it as required.

Setting the available documents is a little trickier. You could probably go with the MultiSelect Field, but adjust the Query part in the blueprint to read files rather then page IDs, however I am not 100% sure it can read form another page. You may have to feed it a JSON list via a route.

Not tested this but something along these lines in your config should do it:

<?php

c::set('routes', array(

// File Links
array(
  'pattern' => 'filelist.json',
  'action'  => function() {
    header('Content-type: application/json; charset=utf-8');
    $files = site()->index()->find('secretpage')->files();
    
    $json = array();

    foreach ($files as $file) {
        $json[$file->safeName()] = $file->filename();
    }

    echo json_encode($json);
  }
),

));

And in your blueprint, (assuming the multiselect can take JSON like the standard Select field)

fields:
  relevantfiles:
    label: File Downloads
    type: multiselect
    search: true
    options: url
    url: filelist.json