This seems to boil down to "I don't understand things written in a language I don't understand" which is fine and all but haven't you ever been curious why so many people will assert it is worth the time to learn?

I think the second part kind of misses the point, as someone in vim has already implemented the feature you wanted, the way that you wanted. So you are basically turning on a parameter.

What is much more important to ask here is how would I implement that functionality [in whichever editor] from scratch, and can I even do that?

That's because EmacsWiki is old, poorly organized and not always up to date. It's to be expected when the area to cover is this huge. "Meanwhile", in recent Emacsen, what you want is

    linum-mode

You can also customize this with

    M-x customize-group RET linum

where you can set font, format for numbers and enable/disable line numbers globally.

Things that look like (a . b) are pairs of things a and b. Enclosing them in brackets, ((a . b)) means making a list, with one element, which is that pair (you need a quote or a backquote before it). (list (cons a b)) is the verbose equivalent. In this case, I think, ".*" is a regular expression matching file names, and temporary-file-directory is the directory for file names that match the regular expression.

This is actually quite nice to customize because you can change little bits of behaviour by just adding another pair (regex . string) to the list. Typing "C-h v backup-directory-alist" also explains what the list is for and lets you customize it with a gui.

The reason the backup-directory in emacs is an association list instead of a simple string is that some people might want some backups in some dirs and other backups other places. More powerful → more complex.

Turn on line numbers everywhere by putting this in ~/.emacs.d/init.el:

    (global-linum-mode)

(Yeah, EmacsWiki is a mess, but that's not emacs' fault.)