Hey mate I am no expert but hopefully this will help. Feet position should be in straps. For comfort you may use the inner rear strap or I have even used the inside of the other side strap when learning and windy. Body position I find for meinvolves me trying to position myself more over the board which generally leads to bent legs. Think I am bending a bit much so try to watch some videos of the good guys to see how they position. Kite bangle changes as generally try to do powerstrokes to get max power and depth or loops to do this. Although for learning I found it useful to be able to bring the kite up to 12 to slow down a little when overpowered. Angle is pretty much as low as possible whilst still riding the fins although with more practice you will work put the angle which gives you the best vmg.