Okay, i'll try to guide you in the right direction. First of all there are a few myths and common advices across the net regarding acoustic treatment, that are simply false. People tell other people things they have read somewhere but never treated rooms by themselves.
1. Low End is the main Problem in every room, that is small (acoustic small!) That is the first thing to treat, everytime! Eq is not an Option. It is simply not possible to treat a problem in the time Domain with eq. "But i eqed my 10 db room Mode at 40 hz, it is great!" No, sorry it is not. The amplitude was lowered to a certain degree and room distortion was added because of the room modes. What you hear, is not the Signal how it was intended to be. It has too much decay. Often described as "Single note bass" in the worst case. It still does sound great to your ears ? Okay, it is fine. Just enjoy your music. Just notice, that there is room for a lot of improvement.
2. Treat corners first.
Simply no. Room modes exist between two Walls, not between corners. It is true, that pressure is a little bit more maximized in the corners but if you only treat them, you are not done.
3. RT60
RT60 needs a diffuse sound field to work. There is no diffuse soundfield in acoustically small rooms (less than 40-50 qm, depends on geometry) Use the spectrogram instead to make decisions.
4.
Choose the density and thickness of the porous Absorption Material depending on the rooms decay in the Bass Region.
Dedicated room 2ch:
5. Start with the Front wall, in my room 40cm of sonorock rockwool was the way to go.(works good down to 40hz) I built modules from floor to ceiling, covered the entire wall. Side walls were treated the same way, except the ER Points. I used qrd diffuers. Back wall depends on what is shown in the spectrogram. If everything is fine. (Max 500ms better lower in the 40 hz region) use diffusers. Otherwise use absorbers with an mls sequence, to not kill too much high tone Energy.
Ceiling is entirely treated with Absorption, except above the listening Position. There is diffusion used. That would be the optimal case, if you have a dedicated room and you can use it for music listening only. How does it sound? It sounds like a high end headphone with much more space, a huge stage without being unprecise. There is only the music and space.
6. What can i do, if i only want to listen to music in my living room ? Without tons of treatment ?
Google for dr. Geddes subwoofer placement guide. You need atleast 3. That is in my experience the best way to get an even bass Response with less decay. It's about stimulating the room modes more even. After that, Experiment with diffusers and absorbers to your liking on the ER Points.
I know this is oversimplified, but it is the best advice i can give to someone new to acoustics. If you want to dig deep, go to gearspace. If you Just want to enjoy your music and do not want to become a nerd, follow my advice. Have fun
Greets