Yes, I think adding a parameter to trigger another pad concurrently is better than simply copying an existing set of data, this way you can play live and use the touch strip etc.
I would suggest the selected master pad sends the following data to the selected slave pad(s).
Trigger/Gate, Pitch, Velocity and Touch Strip Parameters.
Passing slice info would be very difficult to implement in a simple way and its less likely you would use slice on the layered sample in this context anyway.
Another parameter that might be nice for this is a trigger delay. So when the master pad is played or triggered you can offset the start of the slave pad.