Having a grip that keeps the camera as stable as possible is what’s important. I tried a 600 EX RT flash on a couple of bodies and settled on a 5D Mk III since that is the shape of the camera in your photos (no battery grip), and the 600 is the largest and heaviest flash I have.
Keeping in mind that at 6 feet and 200 lbs, I’m fairly big, I felt the camera balanced reasonably well. The heel of my lower palm is supporting the corner by the flash while my upper hand is lifting at the top of the camera near the shutter release and pressing down at the camera right side to keep everything from rotating. That leaves my left hand fingers free to zoom or focus, my right index finger free for the shutter and my thumb free to rotate the command dial on the camera’s back.
No one has ever commented on paper around the flash. I doubt most people even notice. Anyway, it is the results that matter and it is a trick that works pretty well. All my Canon flashes have a wide angle diffuser and a white bounce card built in. the paper is larger pointing in the right direction when the head is rotated. If you want a commercial product, you could use a Gary Phong Light Sphere which is about $80, here, and is inconvenient to fit into a camera bag compared to an elastic and a sheet of paper from a square note pad.
Having a couple of bodies with different lenses is a big help. You spend less time changing lenses as you can let one camera hang on a strap and use the other if the lens is more suitable to the shot. It sounds like your friend is well equipped. Get in as much practice as you can so you are familiar with the gear and can concentrate on the photos instead of the gear.