Some questions about planks

Hi everyone, I've been following a GB based routine now for a couple of weeks, and loving it!

I have been doing some isometric holds as part of my warmup, and had a couple of questions about planks.

I only yesterday realised that they should be performed with legs raised parallel to hips, before I found this out I thought it was odd that the planks should be performed on hands instead of elbows as I find the latter much harder. I assume that they are done on the hands to strengthen the wrist and elbow joints, correct? How should the hands be placed, fingers pointing forwards or backwards? From what I've read (assuming that I've understood correctly) fingers pointing backwards would help strengthen the elbow much more than forwards. How should the shoulders be? retracted into the sockets or extended towards the floor?

Apologies if this has been covered elsewhere but I couldn't find anything.

Thanks Spinelli

Yep, basic stuff for basic strength and circle preparation.

I do them both way for front and rear prone support. Currently, I use a swiss ball and this is probably because I don't feel like bring a panel mat out and I can keep my body bouncing off the ball.