To upload files in Redactor, I use this :
Edit "node_modules/nodebb-plugin-composer-redactor/static/lib/client.js" and add these lines at the end of the file
$.Redactor.opts.fileUpload='/api/post/upload'; $.Redactor.opts.fileUploadParam='files'; $.Redactor.opts.fileUploadKey='url';
Edit "redactor.js" too, and set :
Stop and restart NodeBB.
It's not nice but it's work for me. Editing message seems to duplicate urls... not good.
I'm waiting for an image and file upload in local which can display thumnails, but I'm very bad in JS so I can't help you...