no worries leman.

i'd forgotten about the term playing the piano.
hi actionmax - i'm a bit of a back foot sailor myself, i usually use my front foot on the wave kit.
i think that would be an interesting survey, i know a lot of very fast front foot sailors and a lot of very fast back foot sailors.
the playing the piano concept is really good in helping develop the stance for all of the reasons above. your harness lines should be long enough that your arms are straight. there is an old gauge for setting harness line length. you grab the boom with your hand. the loop in the line should go around your elbow. any shorter than that is probably too short. the exception is in light winds and the boom height will also effect line length.
the hunch back is a result of wrestling the sail. next time you are on the water sailing along push the boom away with your palms and it will help you to straighten and hike out. once you got that position relax.

also there is no substitute for downhaul to allow the sail to twist more and in strong winds just crank it on. having the boom pulled out of your hands can be resolved with more outhaul and inticipating the gusts by reading the winds. even with big sails the effect of gusts hitting in high winds is that you either get lifted of the water board and all or slammed backwards. the sail should not be getting pulled out of your hands. in time you will get that sorted.
this extract is taken from the KA website. although not all sails are built the same it is a good guide generally.
Rigging
as your sailing improves, or you change other pieces of equipment, your sail settings should also change.
Downhaul
The top and leech of the sail are designed to be loose and fall away to leeward, twisting under load. This is achieved with high downhaul tension. It is very common to see sails rigged with too little downhaul tension. You won't pull the sail apart or break the mast, so don't be shy - give it a big tug! Once the correct downhaul setting is found, it does not need to be changed much although slightly (<2cm) less for very light wind may help you get on the plane. The main adjustment is done with the:
Outhaul
Tension the outhaul more for overpowered conditions. Experiment with the outhaul setting in different conditions - it is easier to adjust and unlike the downhaul there is no "correct" setting. Too much tension will kill the acceleration and downwind performance, not enough will cause instability in high winds and lack of pointing ability.
Want more power - less tension / Want more control - more tension.
The correct balance of outhaul tension and downhaul tension is essential for optimum tuning. With time you will develop a feel for your own settings.
Experimenting with different settings will teach you the different feelings and with time you will notice the changes in performance. Once the downhaul is correctly tensioned, minute adjustments in outhaul tension will change the sail's performance.
If the sail feels sluggish and heavy, you probably need more downhaul. If the sail feels light, yet a bit powerless, you probably have too much downhaul or too much outhaul. It's often a fine line between right and wrong setting, so it pays to experiment a bit until you feel comfortable with the sail.