How to display node number in content items that only show up to administrators on ALL content items?
I need it to create links on menu items, to assign blocks to specific
nodes, to create links to content items in articles ect...many
reasons!

You're going the wrong way about this. Having your urls named node/1, node/2 etc.. looks ugly and it's bad for SEO.
What you need to do is give your Content Types an url alias. You don't want your How To Use Drupal article url to be node/1. You want it to be /articles/how-to-use-drupal
You should use the Pathauto module. This module allows you to automatically create an url alias using tokens.
Then when you assign a block, you can use articles/* this will make the block show up on all articles urls.
Pathauto Video Tutorial

I knew about path auto, I just thought it was better practice to use
node items for links and so on, in case I change the page name later,
node number never changes...

You can use the redirect module which will auto redirect the old path to the new path if you change the path name. Thus, you don't have to worry about updating links.
To make life easier, I would also recommend
CKEditor Link - A plugin to easily create links to Drupal internal paths