Re helicopter formation photography (from the ground, not air-to-air shots) - they always look like crap compared to fixed wing, because everyone's got a different attitude (slowing down or speeding up), and the blades are never in the same part of the orbit.
Video is different, generally looks good, but stills aren't real flash at all.
Tac form as I did it was about 2 - 3 rotors, with an arc of freedom so you could slide from side to side as lead manoeuvered - quite flexible and effective for getting everyone on the ground at once.
One of the most important things was to stay on plane (vertically) with respect to the lead, so as not to either get in someone's wash, or hit someone else with your own, leading to overtorques or other embarrassment.
Good fun but!
