If you want to make WordPress as a backoffice system, this plugin can help you disable WordPress features you do not want. It is working great with Disable Blogging plugin ( https://wordpress.org/plugins/disable-blogging/ ).
This plugin can:
– disable pages, media, front-end.
In case that you disable front-end it will be redirect all URL in the front-end to wp-admin page.
PHP 5.5 or higher
WordPress 4.0 or higher