Haha, very interesting way to generate a private key, 20 minutes well spent mate!

Not sure if it's the safest way to generate a private key, but it's definetly the most fun way to do something like that.

Flipping at once would be easier if you could contain the flip, it saves you the motion of flipping them one by one and going around and recording the results is easier then flipping them all one by one.