Turn scrolling combat text COMPLETELY OFF. Healbot shows all the information you need. Combat text is a terrible idea, especially if your UI is overwhelming you, it's typically the worst offender.
Turn party frames off when you're in a raid--there's an option for it under Interface > Unit Frames.
Move healbot over to either side; generally I like to put it on my left side so that the very left bars are right next to my character, so I can see whether I'm in the fire or not.
Healbot has many quick skins options, including one called "Raid" which has smaller bars better designed for 25m raiding. You can also manually resize the bars, the icon display size, whether you display pets etc.