Was hurried in my first reply, here's a more thought-out response.
I am wanting to breed all sorts of shrimp, neos, and caradinas, and one fancy species of shrimp.
Me too, man, me too. I have success with some, but WOW a lot of them don't take off like I expect. Don't discount the idea on my experience, but also don't plan your kid's college fund on it.
my questions have to deal with the ideal setup. I have a 40g stand that I currently have 2 40g tanks on that I was originally going to just divide into 3-4 sections with foam but I know many shrimp keepers have several more smaller tanks. I figure that this is because they can all keep different parameters but want to know more about why they choose this.
More tanks are better. One identical (on the surface) aquarium might go nuts while the other treated exactly the same has no babies.
I am not against having multiple smaller tanks if someone can give me some reasoning. But the way I see it now is that altho you can control each specific parameters you also have to get an individual heater, lid, as well as individual water changes which is obviously a lot more work.
Individual water changes are real, but you get to know each tank you care for and that's part of the appeal for me. In tanks where I use heaters, they are set to 65 or so and rarely turn on so that isn't an issue. My luck keeping shrimp at 75+ has been abysmal and I use heaters only to keep things from swinging too much these days when I use them at all.
I also would like to know how people deal with culls when keeping a variety of different shrimp species with water that doesn't work with the other shrimp.
I have a 125 gallon that all culls go in, they can make it or not. Many I worry won't (like poorly saturated CRS) are still in there and have lived out lives, a year or more down the line. Some I never see again. But I drip-acclimate them all and give them a chance. I realize that everyone doesn't have the option of another tank to drop culls in.