bed is not great but u need that, haha!
Your back wall if the point of first reflection, so maybe put it on the wall under your window? no perfect solution, but could help in one way while hurting your sides, but if u can move it then maybe it would help.
Traps plan sounds good, Honestly for playing loud music in a space like that, as deep as as much as u can trap would be good.
Window, yeah, tackled mine with a few layers of different materials. I was starting with 6 inch layer of rock wool and then a barrier layer and then rock wool again. My windows are on the street but also right behind my main front and center monitors, so I liked absorption on the room side.
I think what u said would work, I would put a layer or a panel of absorption behind a diffusion panel and put that in the window.
I have been using wood QRDs 2x2 and 4x2 size, I usual fill them with rock wool and I have also custom made back boxes that the diffusers slip into and then it is a dual diffuser on front and broad band absorption on the back.
sounds like a goo start u got going. Then think about some ceiling clouds, maybe mixed absorption, barrier, diffusion/scattering.