What results can I expect from egg and sugar variations in spritz cookies?
Powdered sugar would produce a smoother textured dough than granulated sugar, I think, as it would more easily be incorporated with the other ingredients than the larger grained, sandy texture created by granulated sugar.

Egg yolk only would have a higher fat content than whole egg, and the lack of egg white might produce more rich taste, but likely more tender cookies than those with the egg white, as protein in the egg white would hold crumbs together better.