"in waltz. they both start with leading a heel turn, and a step to the side, out of the ladies way. is the main difference just that you turn into promenade as you go out of the move? what about closed telemark?"
Different people will probably nominate a variety of the differences as being key.
Something that can be of a lot of practical utility for the open telemark is to leave the left toe unmoved on the position it achieved on step 1 until it is time to move it directly to the position of step 3, instead of moving it in towards the right foot and then out again.