Initialize WordPress environment to use in a real cron script

I have to run a PHP script through real cron (WP cron being too unreliable). Within that script, I need $wpdb to insert data into WordPress table. But of course $wpdb will not be available as WordPress would not be initialized. Right? So, my question is how to ‘include’ WordPress/initialize WordPress environment to do such tasks? How about
require_once(“wp-load.php”)?

tag search using WP_Query

I need to find only posts with a tag forest gump. I’ve tried: new WP_Query('tag=forest+gump');, new WP_Query('tag=forest gump');. However they both return ALL the posts and not only the posts with forest gump tag. Single tags (without spaces) work fine, though. Alternatives (like plain SQL) will work as well.

Retrieving and Displaying Data From a Table

At the moment, I have created a code that retrieves data from the database and displays it. However, for some reason, I cannot see the files I want to retrieve on my page. My goal is that the data gets retrieved from the database, and is displayed on the webpage. I do not need to make a connection with the database since WordPress does that automatically.