Whatever your place defines as a standard. I’ve seen ugly code in C, JavaScript, Java, etc., that uses them all over the place because they’re not mandatory.

If you don’t have consistent indenting, your code looks like copy/paste from several sources; but if you do have consistent indenting, then the indenting of Python is a non-issue.

Per the Linux kernel coding style:

Tabs are 8 characters, and thus indentations are also 8 characters. There are heretic movements that try to make indentations 4 (or even 2!) characters deep, and that is akin to trying to define the value of PI to be 3.

I’m rather partial to five myself but only when I’m feeling fancy.

Yes

No one will ever know. That is my editor's job. XD

Depends on the mood.