Hello and thanks for contacting us. I recommend you ensure the page is published and in the right development group - active or staging.

In this case you'd need to check the CSS. However, you can always remove something in the live customizer and wait for the preview to load to ensure you removed the right code.

Hello and thanks for contacting us. You can install plugins directly within BoldGrid (and WordPress in general) using the Plugins dashboard section. Please provide more information as to what you're trying to accomplish if this doesn't help.

You can do such testing with Cloud WordPress which allows you to test the plugins together without having to install anything on your local machine or web server.

You can make size changes to the code before embedding YouTube videos but you'll need to edit the code in your editor for videos uploaded to the server.

Hello and thanks for contacting us. As this is a WordPress theme, I recommend you check your widgets settings under Customize or the theme settings.

Hello and thanks for contacting us. I recommend you ensure you have the BoldGrid Staging plugin activated and simply disable BoldGrid Inspirations from your Plugins section. The Appearance tab will then show in your dashboard. Also, ensure all plugins and themes are up-to-date and remove themes you're sure you won't be using - i.e. annual WordPress themes.

You may need to ensure your emails are sent with SMTP authentication using a plugin like WP Mail SMTP as this is a general WordPress issue.

You can read more in this WP Beginner article.