Reply to Mapping idea, modifiers, cross contamination

I'm remapping my MF Classic for cue point juggling and it's pretty smooth so far! Banks 1 and 2 are IG on decks A and B, banks 3 and 4 for cue points 1-8 also on decks A and B. This leaves me with four buttons left over on banks 3 and 4. I was going to map three of them to instant effects, but I wanted one of them to be a shift button for deleting cue points, and toggling the "hold or toggle" state of the effects.

My only problem is that modifiers are global, and I don't know how to track down which ones I can use without screwing up the functionality of my other controllers!
Does anyone know a safe way for me to go about finding out what modifier I can use as a simple "shift" state?

Also, what are some effects you guys like to use over cue point juggling? I already figure on reverb and delay, help me believe of a third one!