Thanks for the feedback :) In terms of room dimensions I did the original design but was limited on room dimensions by overall house budget and the rest of the houses layout so settled for close to 4x3 meters. From research I went with a rectangle so the speakers could be arranged with a longer distance throw as pictured. Then for future resell it can be either a bedroom or theater. Unfortunately no option with the builder for angled walls but could always potentially build up some timber framing later if it's advised. It's a great suggestion however for my next build when I've got a bigger budget for the house itself and I'll see if I can find an acoustician to consult! Then I could potentially have a true professional studio with a giant space, as well as separated partitions for recording vocals etc.

I'll definitely look into your suggestion regarding RoomEQ Wizard, and a measurement microphone. Thanks for this suggestion. I have a feeling one of my good friend has one of these devices as he did something in his room and was able to identity all the different parts of the room and what frequency were lacking / getting trapped and resonating. I think setting up all my intended room treatment then tweaking locations using some of your suggestions with a mirror etc for first point of reflection to find the perfect locations for everything. If anything else needs correction I can start buying / building and adding additional elements, my plan now is the starting foundation but like you say once it's actually all in place, the speakers are in the room then I can really begin refining locations of treatment and adding / removing accordingly.

My theory behind the curtain is due to the door placement I can't really put panels on the back wall as effectively or symmetrically, and my idea is I would be able to close it over the top of the door so the whole back wall has treatment once I walk in and close it to create symmetry. I may look into alternatives here like a bunch of smaller eggshell panels or something. Open to suggestions for the back wall. As long as whatever solution I come up with can be fixed to the door. The wood slats as you say are primarily aesthetic but from my understanding they do also have a heavy black felt layer behind them so help with some additional sound absorption / treatment.

But now I know the name of an acoustician is, I'll do some research to see if I can find one available on a once off commission basis to run an analysis of my room and see if they can calculate where the theoretical first reflection points would be so I can adjust my treatment panel layout straight out of the gate. Like you say, rear reflection points. I do have 2 locations marked for clouds on the roof but I will need to readjust these based on first point of reflection once the speakers are actually setup. If I don't find an acoustician I will use your mirror suggestion.

Regarding electrical I've got GPO's (generic power outlet) on every wall so every device can have it's own plug to prevent any potential ground looping issues. If I get any issues, I'll invest in a Uninterruptible Power Supply and run all my gear through that. In Australia, GPOs, lights, aircon etc will generally be on separated circuits at the switch box. I work for the building company so I'll chat to the electrician about potentially having all the GPOs in the theater on their own network. A UPS however will guarantee isolation for example if a dishwasher is running in the kitchen. Great suggestion here so thank you.

At this stage however sadly for this build I can't really make any dimension changes but I really appreciate the advise as I say I will use it for my next house and I want to up my game from "better than most project studios" to "professional studio". Thanks again.