Another garage studio!!!

It’s been awhile since I’ve been on here so I hope everyone is doing well. A few years ago someone helped design my acoustical panels in a bedroom. I now have got to move out of there and the only place I have to go is the garage. I have a crap ton of acoustical treatment from the old studio and will build whatever else I need. The old studio is 12'x9' . I attached a couple of photos of a crappy sketchup that I did. The garage is and will be used for storage and shipping eBay and Amazon stuff. I dont care about the sound getting out or coming in. I want to acoustically treat the room to have a very good and even frequency listening environment and that is it. I dont do live drums just record vocals, guitar, keys. Obviously do alot of mixing and mastering. The garage 23’x23’x8’3” It has 2 big garage doors on the one side. It’s fully insulated and the walls and ceiling are plywood I have 2/3 of the garage space for selling on eBay, Amazon, etc…. So 1/3 is used for studio roughly a space of 12’x14’ or so I placed 2 different options of desks on the floor so you can see what i'm thinking I’m gonna start with just a few questions 1) do you need to have 4 walls or even 3 walls to make this work? meaning do I need to build a side wall or movable wall 2) can we make this a flat response to record in I know Im missing something but it's been a long day here so thank you for any responses.

you could create some "hard" acoustic treatments (like a slat-slot wall) to form a listening area which has the symmetry you need. the larger more open section can be good for achieving a decent LF response - tbd with testing. the main thing to watch for are odd resonances and noises from things vibrating in the other parts of the room - shelves, boxes, tools etc. i'd set up long ways with back to the large doors and put up a small partition wall towards the window or door on the shelf side so you have effectively a rectangular space - at least 10' deep. the (imho) set up angled slat panels on either side of the new "front wall" where you place your desk monitors etc.