just a quick follow up...
i'm glad you didn't realize it was me in the clip. i prefer honest critisism to false praise any day of the week.
i've never trained yin style BGZ, but yin style seems to use more of a straight spine. so from the point of view of your training you would be correct to say that we're using bad posture.
however the flexed spine is common in many styles of CMA. tongbei calls it "dragon back", we call it "expanding the yang". many southern styles, like southern mantis and lung ying, use similar posture as well as some of the xingyi animals (bear and monkey come to mind).
i'm leaning a bit to far forward, but i think i'm just compensating for the height difference between me and my partner.
as far as controlling the elbows... you're not supposed to control anything during spinning hands training. you have to understand the purpose of the training, which is to understand the changing point of contact, learn to manifest fullness at the point and build power. sticky hand is for control.
we are using a lot of force, so yes it's tense, but in a dense, springy kind of way, not in a stiff way. as i said, one of the benefits of this practice is to build power.
as far as
"When pushing hands neither opponent is suppose to feel each others energy."
again, you misunderstand the nature of spinning hands. as i said part of the purpose of spinning is to understand the changing point of contact and what force is present there. by it's very nature this training is designed to feel the force very clearly, in fact we say that during spinning hands you want to "meet the force", to learn how to "catch the tip of the spear". again, sticky hand is the place for practicing other things like neutralizing, off balancing, etc.
spinning hands, like sticky hand is divided into stationary and moving step spinning.
here's a clip of my Sifu and his cousin playing some moving step spinning hand.