I reckon rear foot first in hard conditions.(Catapulting can be prevented with rear foot in strap; feels safer more secure.(ie which foot would you put in if you could only choose one ?)
Early planing where you aint likely to be overpowered I think its personal choice. You could argue either way ??? (I think) I must agree though you can spread your weight out loads and keep "secure" with just back foot in but I do think all coaching vids argue otherway ???(I`ve spoken to "instructors" who coach differently.?
Purely getting board planing though (and keeping it so) front foot and then put rear foot just behind it. (ie keeping nose down and weight forward helps eraly planing on most boards)(You cant do it when well powered though)
Must vary board to board !