Analyses of a text

For cockroaches, the byword has been: Keep it simple. Consequently today. as always, they can live almost anywhere and eat almost anything. Unlike most insects, they have mouthparts that enable them to take hard food, soft foods, and liquids. They will feed on virtually any organic substance. One study, written a century ago, and still considered authoritative, lists their food preferences as "Bark, "leaves, the pith of living cycads [fern plams], paper, woolen clothes, sugar, cheese, bread, blacking, oil, lemons, ink, flesh, fish, leather, the dead bodies of other Cockroaches, their own cast skins and empty egg-capsules," adding that "Cucumber, too, they will eat, though it disagrees with them horribly." So much for cucumber.

1. I'd like to know if the subject of "adding" is "one study."
2. I'd like to know if "it" indicates "cucumber," "them" indicates "cockroaches", and the clause implies "about the argument?cockroaches will eat cucumber."
3. I'd like to know if I can interpret "So much for cucumber" as "There are so much cockroaches compared to cucumber."

Thank you in advance for your help.