Short answers, pulled from the story.
The corpse belonged to Glyndwr Michael, a tramp who died from eating rat poison containing phosphorus. Military historian Denis Smyth dismissed claims that one of 379 men killed in an explosion on HMS Dasher in March 1943 might have been used and confirmed official records stated Glyndwr Michael was the actual corpse.
Montagu and Cholmondeley filed their plan for Operation Mincemeat with the Twenty Committee on the 4th of February 1943. They created a fictitious identity named Captain William Martin of the Royal Marines to reinforce the reality of the deception operation.
German sympathisers photographed contents but did not open letters while they were in Madrid. Karl-Erich Kühlenthal took documents directly to Germany on the 8th of May after Spanish authorities removed damp paper by winding it tightly around a probe into cylindrical shape.
Grand Admiral Karl Dönitz met Hitler on the 14th of May discussing progress of war and Hitler ordered Greece Sardinia and Corsica defended at all costs. By end of June German troop strength doubled on Sardinia to 10,000 while seven divisions transferred to Greece.
The body was found at around 9:30 am on the 30th of April 1943 by a local fisherman. It was taken to Huelva where Spanish soldiers handed it over to a naval judge for further handling.