The Horus Heresy cycle is a good way to start. It is 10 000 years before the “current” events in 40k and explains a lot. But it is in of itself a big pile of books. I would say, read the first 3 and then pick whichever book interests you next.
Methane is broken down within 10 years which is pretty short. Yes, the other environmental issues are real. BTW, I am eating less and less meat. I just see a lot of false assumptions regarding carbon in the atmosphere.
Every time I read about meat and greenhouse gases I feel the need to explain the natural carbon circle. A cow does not produce carbon. It takes carbon from plants and releases it to the atmosphere. Then plants retake that carbon.
Humans are adding carbon to the atmosphere by digging out stored carbon from the ground and bring it to the atmosphere.
So we have to fix the part where we bring additional carbon to the atmosphere. But yes, there are other environmental issues with cattle if you read the op’s article.
The Biogenic Carbon Cycle and Cattle: https://clear.ucdavis.edu/explainers/biogenic-carbon-cycle-and-cattle
Hiking, running or trailrunning
Adding the refiner to stable-diffusion-xl-base-0.9:
No, I think this is one if the best starting points overall. I hope you are going to enjoy it. 😀