There were two questions. Voice layering and notes to add. I like the "beauty" of the resulting sound when some combinations of two or more patches/voices are layered. Will not check out every combination on my keyboard to experiment. Looking for some general rules/examples of combinations that work.
As far as notes added, I know there are several little things, unknown to me, that can be done to dress up a very simple melody.

I am, in this question, not trying to become a better player. I want to enjoy the sounds that I make on the keyboard. I am 77 and not going to improve my technique or repertoire much at this point. I want to enjoy myself at the keyboard.
regards, chuck