Key-settings, Macro settings, Interface settings.

Right. I'm non boxing while my computer is being fixed and I wanted to spend the time to fix out a lot of interface settings, key settings, and addons. But my question is - If I change all keybindings, interface settings, and custimize my interface on one character. Is there a way that I can fiddle around with the folders and copy the settings to all my accounts? I know this was possible "back in the days" but now days Wow macros and stuff run cross-computer so is it still possible?

And, how will my addon settings look like if I fix it all now, and then copy the hole folder onto the computer when it gets back. Will it look the same?

Some will work that way. You can copy the interface/addons folder or just copy the whole WoW folder. I think what you are talking about is the server side stuff. That won't need to be copied as it is tied to your team no matter what computer you use. I think it might want the same addons in some cases, but overall it should work. If nothing else you get practice while you can't play.

Quite a few settings are for the entire account.

Others can be copy/pasted from within the WTF folder.
Some of these will be saved for the account, and can be copied to other accounts, while others are on a per character basis.

Also, if your software option supports accurate mouse broadcasting (or if you add an HKN (which is free) script for mouse broadcasting), you can turn broadcasting on and then just re-click every option you have selected for your configured toon, so the other toons receive the same options and selections.
Game elements are for the most part in precisely the same position on each screen, so as long as the UI elements are aligned this is a relatively easy/quick fix.
You can also configure an entire team at once like this.