I tracked the problem of my Diplomacy issues. In my CIV4DiplomacyInfos.xml, I had an extra <Response> tag at the beginning.As for the UI, I retraced my steps inside this forum and did what nahuiocelotl suggested in post 580. I alt-tabbed out and upon returning to the game, the UI had magically reappeared. It's been 200 turns with the AI in control and things are going smooth. Now I just need to get Meiji, Hitler, and Ho Chi Minh working as leaders and things should be well. Thank you again.
Edit: The tech tree is stuck and will not show me how many turns each tech will take nor allow me to scroll into the future era techs.
Hmm, if you're tinkering with the mod yourself, it becomes tricky to help you...

Do you have BUG installed in the Custom Assets? If you do, that might cause some issues. BUG is completely integrated in my mod, and if you have an extra copy interfering, I'm not sure what could potentially go wrong.