ANSWER: Some of u got it right.But it was heartening to see the attempts and the thought u put to it. Which shows how much can be understood in the headstand and to learn to hold it right:)
INitially, by mistake, the beginners take the weight on the neck. The actual weight or hold -- in salamba or supported headstand -- is on the elbows. The complementary support -- just because it is any case on the ground -- comes from shoulders.
The stomach should be firmed -- if it flops, the weight again shifts to neck. The body will feel heavy and u will either hold it with strenght (which is not required for it after some practice) or u hold it uncomfortably -- which is not the nature of the pose. In either case, coming down can often be uncontrolled or shift. If the stomach is firmed -- by merely focusing on it:) -- u will have better control over the pose. Also, if the stomach poops in front - the curve of the spine becomes very intense and pressure also shifts to lower back, giving u a tight back...
When the elbows and shoulders support u well, u can even extend the neck (what i call creating a space where none is -- this is the philosophy in some martial arts also) and actually lighten up further in the pose!
Though a lot of schools have a lot of variations of breathing there is one movement of the breath (inhalation-exhalation) which is used in difficult part of the pose? Can u think which u must use to deepen a pose -- an inhalation or an exhalation? Why?