Check out the FAQ section for answers to most of your questions, as well as the various /chatcommands available to the user interface!
There's a selection of my own all-purpose addons that I recommend using along with DiabolicUI. I am using all of them, and the development is based on people having them. I also highly recommend Munks brilliant addon Immersion, as it really fits the feel and style and experience of this user interface.
- BigGameMenu: www.curseforge.com/wow/addons/biggamemenu
- BigInputBox: www.curseforge.com/wow/addons/big-input-box
- ChatCleaner: www.curseforge.com/wow/addons/chat-cleaner
- CleanWorldMap: www.curseforge.com/wow/addons/world-map-shrinker (Retail)
- EnhancedWorldMap: www.curseforge.com/wow/addons/enhanced-world-map-for-wow-classic (Classics)
- Immersion: www.curseforge.com/wow/addons/immersion
The UI can be externally tampered with through third party addons, and unlike its previous versions, this one encourages it! Currently only a few of my own extensions exist, but I hope to both make many more myself and see multiple ones from other authors as well.
The idea of these extensions is to add features I don't want cluttering up the base version and modifications and edits that only suit a few, without having the base version grow to a bloated monstrosity of settings and confusing menus.
- DiabolicUI Chat Mover: www.curseforge.com/wow/addons/diabolicui-chatexpander
- DiabolicUI Goldpaw Edition: www.curseforge.com/wow/addons/diabolicui-goldpawedition