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Not much. At official google's ADsense page you can check the average payment.

It will vary depending on visitor's region, content, etc. Check information here:...

Google ADsense is the Google's way to give you money for showing ADs in your site.

ADSense has the feature that your visitor do not need to click your AD in order to monetize your wallet. But...

It is complicated.

In order to upgrade WordPress or any plugin, it is needed to make all plugins inactive and active them slowly. If it crashes you can backup your site with a Backup like Backup...