I'm quite a beginner in Joomla; only designed 1 website so far; but the whole setup / domain name + web hosting configuration and lock of the frontend was made in advance for me; so I'd really like to know how to do all of that in the safest and easiest way on a mac with the newest version of joomla. I work on a macbook pro, version 10.13.6. I really want to create a administrator (and locked frontend) page which I can access from any computer to work on; so I guess the solution via XAMPP is not an option..
So why not just set the page in the joomla configuration to „offline“ or did i missed something in your question? Its exactly for this purpose.
There is a plugin called n3t coming soon which may help you with this. When enabled it will show a coming soon page (which you can customise if you like) while letting you view the site. It uses your IP address to decide whether you can see the site or not.