Answer to: Do I need to replace the LCD screen and touch screen separately?I answered this a little more in depth in another question here but no, you don't have to replace the digitizer + screen together. You just have to pry tabs around the edges of screen to work the digitizer apart. That is assuming your digitizer is still good and working.
Answer to: Is there an already fused gampad/digitizer assembly?Just took my LCD apart. Not sure where this "fused to the screen" business came from (yes, I saw it in the tear down as well). You just pry around the edges of the LCD to get the digitizer off.