To reiterate what others have said already: There is really not much wrong with your riding. There are some areas for improvement - slightly more athletic stance (i.e., bend more at ankles, keep, and hips), slightly more weight forward, slightly less open upper body (that seems to be the case only occasionally) - that will all help reduce/eliminate some of the slight ruddering, but nothing dramatic at all.
Also, I do not think the board is too short for you, but it may well be too wide. Close-up pictures would help, but from the video it kind of looks like there is not enough overhang... If that is the case, it will make it difficult for you to put sufficient pressure on the edge - which does seem to be an issue in both videos.
cheers hktrdr. When you say "slightly less open upper body" are you referring to when doing the toe turns fro example, my upper body shouldnt be facing up the hill?
regarding toe overhang, the boots that I'm wearing is a size 9 (mens) nike kaiju. I've always thought that i have enough overhang for the board that I am wearing but I stand to corrected if thats the case. here's a couple of video that perhaps makes it clearer:
To add: Your friend's board looks way to wide for him - the toes of his boots do not even appear to reach the edge of the board, let alone have any overhang at all.
Compare your (and his) set-up with the other rider around 3.30-4.15 in the first video.
I will let him know about this, thats probably why he has a lot of trouble with initiating turns.