Installing a UI with multiple user accounts question
 

I have been looking into installing a UI, but my question is....I have 3 different user accounts on the same computer, and they are not all mine. If I install a UI will it affect all 3 users? I would be the only one wanting the UI. I have been searching for an answer and cant find one. Any information would be greatly helpful. Thanks so much in advance.

When you install addons everything that you put in the addons folder is accessible to all accounts that run wow from your computer. If the other users wouldn't want to use specific or even all of the addons you've installed the other people can just disable them at the character selection screen by clicking on manage addons in the bottom left corner of the screen.

This ^^

The addon settings themselves are stored in the WTF folder on a per-account basis.