Got the Room! Construction starts next week! Opinions Needed

Ok guys, so i finally got the room! the room is underground and we'll start construction for isolation next week the measures are all shown on img_01 and the idea is basically this: The grey walls on the image are the room's original brick walls. The blue window on the back (the 3,78m wall) is already there. That small 1.22m room is the bathroom. the room is 3m high, but there's a small catch on the roof, shown on img_02... i'll get back to it. what we're probably gonna do (unless advised otherwise :wink: ) is build a second wall using gypsum boards and rockwool (shown in green) with a 10cm gap from the original wall. as you see, the wall where we'll install the glass and the door still doesn't exist, so that will be a double GB wall with rockwool inside. so, on with the questions. what should i do about the huge window on the back? you guys think that covering it with GB + rockwool will be enough? On the other side, when i install the double glass, should I angle it in some way? Also, I was thinking about covering the gap with some foam, is it a good idea? The door... ahh the door... I'm worried that GB won't hold a heavy acoustic door, so my idea was to use 2 doors, one on each layer of the GB. Use rubber to seal it on both doors and use rockwool covered with any kind of cloth or fabric on the inside of each door, any decency to that idea? And getting back to the roof now. As you see on img_02 and img_03, there's this "L" made by a concrete column that crosses the room on both sides and I'm really lost with what to do with it, what do you guys recomend? I considered lowering the whole roof, with would make the roof TOO low, leave the gap 10 cm from the column, which would make it 30 cm from the rest of the wall, taking too much space, following the "L" with GB which i'm not sure is possible... what do i do? sorry for the long text and so many questions and thank you guys!! PS - Guys, nevermind the 3,19 measurement on img_03, thats a mistake, its actually 2,99!