Hi tomass,
Thanks for your patience.
1. Header
+ Menu items: You can go to Dashboard > Theme Settings > Typography > Advanced > there you can create a new Rule by clicking on + Add Rule > then select Main navigation links from the dropdown > then you can define the Color and another font styling for these accordingly: https://snipboard.io/xkdpBr.jpg
+ Icons: Use Custom Selector and assign elements like screenshot https://prnt.sc/n-mrqMBAIKa2
.whb-col-right .wd-tools-element > a
You can read more about Advanced Typography here: https://xtemos.com/docs-topic/advanced-typography-settings/
2, 4. Blocks
You can create a dev site and import any template there, then with the help of the import functionality of Elementor you can copy the some specific blocks and move it to the main website, more detail is here: https://elementor.com/help/template-library/
Devsite – also called a Staging platform where you can test issues, enable/disable features/plugins thus such changes will affect the main site. The below article will help you to create it:
https://www.wpbeginner.com/wp-tutorials/how-to-create-staging-environment-for-a-wordpress-site/
3. You should deactivate all plugins (except Required Plugins) and then reactivate them one by one. This makes it very easy to isolate the plugin causing problems.
Regards,