Well I can speak to the 2nd question. Disclaimer (I am not a mid to large scale breeder, I average 8 rodents a month). In order for my girlfriend to agree to allow me to breed at all I had to have a good plan for euthanasia. I am not worried about costs one bit so I found what I considered to be the right way to do this and I started working toward that goal. What I did was went to my local welding supply store and bought a 5lb CO2 canister. This is expensive up front but refills are cheap. What I still need to do is plunk down some more money for a fitting that will connect to the canister and some aquarium tubing. I am using some clear plastic tubing used to connect an air stone to a small air pump. I have a fitting that give me a decent connection but there is a small leak. Next you need the chamber. I just use a sterilite tub. Since CO2 is heavier than air there is no need for a tight fitting top. I use a rather high tub to allow for a good cloud of pure CO2 to form in the tub. I then used an old soldering iron to melt a small hole in the side of the tub near the very bottom. I make the hole small at first and expand till I can cram the plastic tubing in. I have thought about using hot glue to seal the edges. That really about it. In order to absorb the urine I put some wood shavings in the tub before I use it. Now if you are euthenizing a large number I think a wire mesh would be perfect. I would just put a few spacers down in the tub then set the mesh on top of that. The only really expensive part about this is the CO2 canister. I think I spent around 65 for mine. If you want to do it right a regulator would be nice too.