Hello Lozzie,
I have done a lot of time helping beginners learn to land, remembering that I had a hard time getting it. And that was in a C152, not a glider.
In your detailed checklist, you are WAY OVERLOADED with detail.
Learning to land a glider keeps it simple. and then going on to do the landings in power, why you've got the basic approach and touchdown NAILED!
As the most important thing is to LAND SAFELY, work on that first.
Later on you can work back onto the other stuff, like circuit planning, decision heights, engine management, radio yak, etc. All these details lead up to the landing. If you get the landing wrong your instructor may not be impressed.
SO, assuming you have somehow turned all the corners and are lined up on the approach, this is where SPEED becomes critical. Approach speed must also be nailed....appropriate for conditions of the day. Strong winds? you will need to safely get through the wind gradient, so a faster approach is used. The same strong headwind will be useful as your over the ground speed will be nice and slow, so gentle touchdown is possible.
Light winds require accuracy. Your instructor will tell you the best approach speed for the type of aircraft you are using.
The idea of a landing is to aim at the ground and just miss it. Otherwise you would be stuck in the ground like a spear.
At what point to begin the roundout - also called the flare. THIS MUST BE DONE GENTLY, NOT ALL AT ONCE.
So in the training K13 glider, I recommend beginning the roundout at the height of the average elephant. Look well ahead, don't look down.
Raise the nose a bit and wait. Raise the nose a bit and wait. and do it again and again until you are flying just above the daisies in LEVEL flight, with the wheel just above the ground. Wait some more, and as the aircraft gets slower, it will gently no longer be flying and gently touch the ground.
The FLIGHT IS NOT OVER until you stop moving, so remember to keep straight with the rudder and keep the wings level.
That's all there is to it! Works for any aircraft.