"Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms" by Dr. Floyd Toole, Third edition.
https://www.barnesandnoble.com/p/sou...YaArSAEALw_wcB
You may be surprised how little you really need.
Places that sell acoustic treatment (like GIK and Real Traps) want to sell you lots of acoustic treatment, what a surprise.
Eliminate the red "star" shapes to the left and right of the speakers, that's not where diffusion goes and bass traps go in corners, not behind speakers.
Old school concept is LEDE and RFZ (Live End Dead End and Reflection Free Zone) which is what most acoustic treatment guys want to sell you.
Don't start buying stuff until you read the book. Home systems are not recording control rooms.
And, first off, your speakers should be on the short wall firing down the long wall.