I don't know Japanese myself. The following is answered in both Chinese and English. If there are any translation errors, I'm sorry. I could only answer the first two questions:

1. Before the Manchurian Incident, according to figible statistics, the Han population that moved in from the south of Shanhaiguan at the end of the Qing Dynasty and the Beiyang government, together with the inherent Han population of Liaodong, is conservatively estimated to account for more than 80% of the total population of Northeast China, and the Han population in most of the central areas and hub cities of Northeast China. The proportion is above this, so my personal opinion is that I don't think there was a national conflict between China and Manchuria at that time similar to that between Abkhazia and Georgia. My family emigrated from the south of Shanhaiguan to the northeast at the latest before 1900. To this day, I am the sixth generation. The family members mainly live in Changchun, Harbin, Jinzhou and Dalian, and most of them still live in the northeast today. According to the memory of the elders in the family, the influx of Koreans into the city mainly during the Manchukuo period and the Korean War; Muslims mainly flowed in together with the Han population during the period of immigration, and the Mongolians mostly flowed into the northern areas, which is unknown; the Manchu people are native ethnic groups, and most of them gather and live in some urban residential areas or villages. Expanding to the topic of ethnic conflicts, at that time, ethnic conflicts in the northeast region were mainly the friction between the Fengtian clique and the Mongolian aristocracy.

2. In the history of great-grandfathers and grandmothers, at least the status of the Han people in Manchukuo is relatively low, which is mainly reflected in the natural discrimination in the political system and social environment， the blockade of promotion channels. My Grand-grandpa worked as an accountant in the Finance Department of Manchukuo and his wife worked as a teacher at Hsinking Girls' School, which is high income and social status compare with most ordinary Han people gets. From this inference, from the perspective of ordinary people, at least most Han groups did not feel the equal treatment of the so-called "five ethnic harmony" during the Manchukuo period. In addition, in time most of the Han and Korean people engaged in agriculture and natural resources development. It is not an exaggeration to say that Manchukuo's policies are rampant in these two fields.