How to build a simple content approval workflow between an administrator and a user?
Have a look at my answer to "How to implement a multi step approval with webforms/entityforms based on form components?". It explains how you can implement a workflow that is pretty (though not exactly) similar to what you are looking for.

To do so, it "only" requires you to use these modules (and regular content types):


Rules.
Node Convert.
Flag.
Content Access.


Use such approach, it does not require modules like "Webform" or "Workbench".