how do you position your front and back hand, backwards forwards, wider, narrower in different wind strengths? for example light wind when starting pumping versus flying and so forth?

I find I tend to move my front hand towards leading edge once I get on foil, more so when fully powered.

I found it depends on which wing I'm using, for example when I had the Airush 6.0 I would pump with my front hand forward and then move it back once up on foil, the wing started and tracked better that way, with the Unit 6.0 I don't move my hands at all

Riding toeside I found the twist in the shoulders uncomfortable, until I started moving my front hand towards the middle, now the back hand just steers and holds less power

Depends on your wing and your level as well. Grab from the very front of the front handle with your front hand while not yet foiling, and move it gradually further back while your speed increases. With nice wings you can easily slide your hands while pumping the wing. By moving your hands in the handles you can affect the angle of the wing, and this regulates how much power you have in the wing. There is no point to have too much power while you are not yet moving. And once you are already moving, at some point the apparent wind starts to kick in, meaning you could afford to sheet in the wing, but instead of sheeting in with your back hand, it's much better to slide the front hand further back in the handle, and that would change the angle of attack of the wing the same way as sheeting in with your back hand would do. That allows your back hand to stay extended and not bent. Much more natural and not tiring, no need for the harness to cope with the excess power, etc. That method is also good for pumping a fairly big wing without the wing touching the water, but it works the same way with the smaller wings (that would not have the problem of touching the water) as well. Here's an example with a 6.0 m2.