IF I make my margin in two steps (4" and 10", will it be that when ice about 8" settles on the first step that the ice will damage the liner or, as I hypothesized before, pressure rocks under the ice against the liner wall, maybe cutting it if its fieldstone.

I have parts of my pond that are shallow enough to freeze solid in the winter down to the liner and have not noticed any liner damage. That's not to say that it's impossible. Again, I wouldn't worry about it.