Copy and paste puzzle

Hi y’all. I have been busy trying to animate some photo-puppets. For instance, I want a character walking towards me. I’ve found the most effective way is to shrink and expand the legs with the transform tool. I start with one leg up and down, then the other leg, I try to get the smoothest motion as possible, it ain’t easy! Finally, when I get a section that looks good, I click on the first keyframe, and, holding down “shift” I select the final keyframe. The area is selected I then Ctrl-C (copy) and Ctrl-V (paste) to the next appropriate frame - say 10 frames - darn, the area is right up against the last keyframe. How do I get it to leave a space? Also, is there a way I can I paste multiple times i.e. “paste 20x”?