would sage clash with: sharp cheese w/dill, mozzarella, swiss? thinking quiche to use up sage and ends of cheeses. also may use squash & leafy greens?

Sage lends a savory note, so anything savory, like sausage, as Sam1148 suggests, and the heavier greens. Dill has a brighter, lighter note. It goes nicely with quiche if it features a lighter squash, like zucchini.

I'd drop the dill and add thyme. Maybe some chicken sausage, or pancetta. Kale or chard, and mushrooms. With a Gruyere cheese.

Would Caesar clash with Pliny? Unless it's a low moisture mozza I would leave that out. Sage and dill are not really complimentary flavors, myself I'd choose one over the other and probably not dill.

I don't think it would clash too much with the dill, if that's what you mean. While sage is an unusual choice for quiche, it will be nice with the squash. Go for it if you like the flavor.