Hello, my first question is: Do you want to leave the foot on the peg like in the hang five when you start the whiplash? That means "hang five to normal whiplash" for me. The other option would be to put the second foot on the other peg and let the frame rotate in the other direction. This would be "hang five to opposite whiplash" for me.
In both cases having your foot in front of the seat when the frame starts to whip or behind the seat/backwheel is basically personal preference. I have the foot in front of the seat and think it looks better.
Definitely you should be very safe with hang fives!
I would say that you can do both directions of the whiplash without any carve from a completely straight hang five. The idea (for me) is to let the seat loose the contact to your butt (let the bike go a little down whereas you body stays in the same position) and at the same time "kick" the seat with your butt/inner leg to the side to start the whiplash. It is important to try out how you need to lean the whole bike (more to the left or right) and how much you need to push the bars forward.
I can do the normal version, the one with the opposite whiplash is much more difficult for me. I pulled that too here and there but typically cannot do it.
Keep patient and have fun!