Creating and Using a Development WP site

I consider myself a ‘novice’ at WordPress and am trying to learn this as I go. I have a good understanding of PL/SQL and minor html.
My question is just like many others I have found on the forums.
I have created a public ‘LIVE’ website and would like to make some improvements for a future release all at one time.
This would include making cosmetic changes as well as additional functionality.

So I have a few questions:
1. I have not found a complete step by step listing of what to do to make a dev environment.
I followed the steps in https://www.ads-software.com/support/topic/duplicating-the-existing-wordpress-site
and for the most part, it is up and running, but not all the items (such as menu items, etc) are pointing to the the new install.

2. Is this the ‘best’ methodology for accomplishing my task?
If not, what would be a recommended ‘best-practices’ for this?

3. What would be the steps for moving the ‘dev’ site back to public or ‘LIVE’ ?
Would simply moving the WordPress Install be enough or would there be modifications to the wp-config ?