Questions about rise and oven spring and degassing

I think I'll explain my procedure and tell you as I go where I  have questions for my 40% spelt, 40% kamut, 20% rye bread:

After having mixed the amount of preferment required in my recipe ( 200g in this case), I let it rest until it has at least doubled ( sometimes it will triple if I did not stick around).

Now I do a 1st build, hand mixing  1/3 of the total flour  and water into the preferment and let it rest again until it has at least doubled ( abt 3-4 h). Then comes the second build: I add the remaining 2/3 of flour and water and all the other ingredients ( salt, honey, sunflour and pumpkin seeds that had been soaked overnight, plus fennel and anise seeds etc etc); let it all rise again until it has doubled ( after about 3h).

Next I will do one  stretch and fold which degasses the dough as I form fit  it into a glass baking pan . ( I used to do 3 stretch and folds, in 15 min. intervals, but found no difference in the bread, so I cut it down to one.) 1st question: in some places I read the importance of degassing and punching the dough, in others I have read to handle the dough very gently when forming it into a pan or shaping it. Which is right at this point of my procedure? Punching and degassing or gentle treatment?

Again I let the dough rest until it has almost doubled in the pan, perhaps in abt 1 1/2 h. ( I am saying "almost", because I am trying to fit it all into one day: starting with the preparation of the preferment at 8:00 a.m., finishing with taking the baked bread out of the oven when I am close to ready to go to bed). I have noticed that if I then put the pan with the dough very carefully into the preheated oven ( no shaking here or else it all collapses, never to rise again), there is only a little more rise happening in the oven in the first few minutes. Is this how it should be? Other people talk about great oven spring, where is mine ???  Has the yeast spent itself earlier? Should I perhaps not let the dough in the pan rise as  much as I do, so it can rise in the oven? 

My fiance used to bake bread with commercial yeast. He used to put the dough with the pan in the oven while the oven was heating up, and get a great rise. This is what I initially tried doing with my sourdough, the dough would rise well in the oven but I found that the loaf was develloping big cracks  along the sides ( inspite of my slashing at the top).  Now I preheat first, no more cracks, very little rise. 

We enjoy our bread; it is a bit dense, which may be partially because of the home milled flour we are using. I cut it in thin slices, similar to pumpernickel.