1) Have you looked at the split screen examples?
I don't see any reason why the tabbed screen contents have to be g-code/machine path views...
2 & 3) As I'm going through the process of making my toolchanger far more useable, I've hit similar snags. For debugging, I just run KMotion in the background with the console open. My view is, provided the toolchange routines are working properly, there should be no need to see any console messages. Any information/warning to the user should be via a message box.
As for showing what KMotionCNC thinks is in the spindle, are you tracking this in the KFlop? I've got 3 global vars I use to track the tool changer, so those can be shown in a DRO.