Very nice shots. Wish my cats were half that coperative.
Interesting topic. Coming from a D700, where the only use I had for the pop-up was for commander mode. It did a poor job for a flash even fill in. If I need a flash, I use my much maligned SB900. For fill in I use a SB400. Have been experimenting with the high ISO'so of the D500. So far I am impressed at it'seems ability to take decent exposures where my D700 couldn't focus without the focus assist lamp. I don't miss the pop up. Prefer having a 100% view finder an having the SB 400 in pocket if needed.
Cameras have either a mechanical or electronic shutter.electronic shutters tend to give a long lag time from when the shutter release is pushed and the picture is taken. A problem with a moving subject.
THERE ARE many good suggestions so far. You also need SD memory cards for your new camera. The memory card needs to be formated in your camera to have the correct file structure.
HAPPY SHOOTING