Regarding point 4: they were kanji "puns", so to speak, regarding the names of China and Korea in Japanese. Normally they're written 中国 and 韓国, respectively. The names mean "Middle 中 country 国" and "Korea 韓 country 国", pronounced "chuugoku" and "kankoku". The tweets the author made replaced the first characters of the respective countries with characters that have the same pronunciation but different meanings, 蟲国 ("bug" and "country"), and 姦国 ("rape" and "country"). Both are still pronounced as "chuugoku" and "kankoku". This is extremely offensive, somewhat like calling Nigeria "Nigger-ia".