Short answers, pulled from the story.
The majority Bamar community supported the Japanese because they were restive under British rule and unwilling to defend the British establishment. They joined movements aiding Japan due to concerns over Indian labor importation, land mortgaging to moneylenders, and erosion of traditional society.
The Burma Independence Army was officially founded on the 28th of December 1941 in Bangkok Thailand. It initially consisted of 227 Burmese and 74 Japanese personnel before expanding significantly upon entering Burma.
Lieutenant General Thomas Hutton commanded the Burma Army with its headquarters located in Rangoon. He had only the 17th Indian Infantry Division and 1st Burma Division available to defend the country against the advancing Japanese forces.
At least 500,000 civilian fugitives successfully reached India while an unknown number conservatively estimated between 10,000 and 50,000 died along the way. Many survivors suffered from diseases such as dysentery smallpox malaria or cholera within months of their arrival.
The Japanese occupied Kalewa on the 12th of May 1942 after covering distance in 127 days fighting 34 battles. This occurred shortly after they attempted to surround the Burma Corps crossing to Kalewa by ramshackle ferries on the 10th of May.