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Yes. C is for center.

No. The width is one time the width of your text width. The width of the page minus the page margins.

What Stefan meant to write is: Use oneside or openany.

Plaese also have a look at the quick guide, specifically this.

You do know the number right now at this moment, but it can change later. LaTeX keeps care of that for you using the aux file. It's a nice feature. Think about your table of contents at the very beginning of the document. If your document gets longer, so that the table of contents needs more vertica...

They are a natural byproduct to produce your pdf. The files contain important information. Just keep them. The log file keeps important information needed for debugging the document. The aux file keeps track of your labels and citations. The sync files sync source and pdf-output of the editor/viewer.

There is no difference. One percent sign starts a comment.

welcome to the forum.

It is an option for biblatex. Please have a look at the package documentation.

maxbibnames=99

\ohead[]{\pagemark}\cfoot[\pagemark]{}

Should work