So, moving on I managed to put up the left wall's insulation, and I did add in the little stud support in the centre panel. However I didn't trim down the 60cm wide earthwool so it was much more bulky than the other side.
Which I would live to regret as I struggled to fit the board on. I persevered though and a number of the dry wall screws just popped straight through the plasterboard as too much wool prevented them from securing flat to the wooden beams.
I just couldn't get the bottom left corner to slot into place so stupidly tried to shove it with a 2x1 only to rip through the bottome corner. So I unscrewed the board, reset it so both edges would slot into places and rescrewd it into place. I'm hoping I can try and make that bototm edge more solid iwth some PVA or I may have to reconsider adding a skirting board afterall.
The following night I was able to get the top section in place. I'd added a lot more staples to the earthwool so there was less pressure to combat. Measuring was pretty much perfect with the only cock up being I fogot I had to trim 6 or 7cm off the top edge and did all my measurements and marking only to have to cut them off and redo them! But the board went up perfect after this
I even added a few extra 2x1s to the back wall. I keep convincing myself this will be easy to do as I only need to trim one edge of the board. The back wall is 3m long and each board is 1.8m so I just need to trim 30cm [give or take depending on with peice of wood I attach it to] and the bottom two panels will go straight on, but then I forget I also need to put in the markings for the screws which will be about 15-20 minutes and then I'll need to measure, cut the insulation and then tack it in place that'll be another half hour no doubt, particularly as there is a diagonal strut through the two end pieces and also the middle space is pretty wide so I'll have to crack open a new roll of earthwool. So 'straightforward' it maybe but I'm not so sure it'll be quick.
Then I've got to add the two panels on top, which will require a little trimming to accommodate the sloping roof and then a couple of wedges on top to handle the Apex, which worries me a little as again I'm not sure about the width of wood I'm going to fix to...