So, usually christmas cake recipes call for  wrapping paper/cardboard around the cake to insulate it a bit. (See this question: Why should I wrap a cake tin in newspaper?) I find myself lacking in newspaper but with a plethora of shipping boxes due to all the online purchases I've found myself doing recently. I happen to have a box that would be the perfect size (small enough to fit in the oven, but big enough for the cake). And also this seems like a great lazy person solution that appeals to me. To be clear, I mean to put the Christmas cake mix in the baking tin, and then put that in the box. Given the box is devoid of plastic (paper tape and cardboard only), and isn't touching the element (obviously), would this be a viable method? Anything I need to keep in mind? My plan is to close the box entirely top and bottom and interleave the flaps so that nothing comes open. Particular concerns:  The box catching fire The printing on the box releasing chemicals into my food The oven convection being impeded  Any reasons why this is a bad idea? (My cake is currently in the oven, I jumped ahead a bit and then thought maybe I should check anyway. It hasn't caught fire yet). (Also, I did also see the reduce-by-15C-forgo-the-box-entirely method, but my oven only goes down to 140C, the next step down is 100.) 
Your dough should be fairly flexible by the time you are ready to stretch it.  I regularly make Neapolitan style pizza, and use a long ferment. It sounds like you are on the right track, and your photo looks like a good start. Each time you manipulate the dough the gluten structure tightens and the dough becomes more difficult to shape. I would recommend that your next step be portioning.  That looks like enough for one or two pizzas.  So, step two is creating balls of dough.  Then let those rest at least 30 minutes, but up to a couple of hours. Next, when shaping, work as gently, but as quickly as possible.  Do not use a rolling pin, as this will keep you from having a crust that is puffier than the center, if you are making Neapolitan style.  Begin on a well floured board and use your hands.  There is some technique here, and you probably will want to find some videos to help. By the time I get to this point, with proper resting, my dough springs back a little, but not that much.  It readily holds its shape.  I begin on the board, then lift and use my fists to stretch the dough into shape.  That took some practice. If you are making pan style, a rolling pin will not be helpful here either.  Instead, begin to stretch the dough a little, then place the dough in a well-oiled pan, well ahead of when you want to top it.  Gently use your fingers to spread the dough.  When it begins to spring back, set it aside.  Allow it to relax, then repeat after 10 to 15 minutes.  Some styles allow for another rise in the pan before topping and baking. In general, pizza dough always wants to spring back some, but allowing the gluten to relax and learning to work quickly will help.  You should certainly be able to get to a point where it is not an issue. 