UI is user interface. The default Skyrim inventory screen is abhorrent and I was so happy to change it. It was made that way to work for the console ports but it's really just horrible for a PC user.
Torrenting is usually pretty safe if you use well known sites, popular downloads, and don't go too close to the back alleys of the internet. Your AV will sometimes get a false positive for a trojan hidden in your download but this is usually caused by a cracked .exe file (that lets you play without a CD) and is actually safe. Of course it's always a good idea to scan anything you just downloaded anyway.
However it is easier to mod with a Steam purchase of the game anyway.