Short answers, pulled from the story.
The Territory of the Military Commander in Serbia existed from April 1941 until October 1944. German forces crossed into Yugoslavia on the 6th of April 1941, and the administration evacuated during the Belgrade Offensive in Vienna October 1944.
General der Flieger Helmuth Förster became the first military commander on the 20th of April 1941. He reported to the Quartermaster-General of the OKH and resided at headquarters in Belgrade.
The Commissioner Government formed on the 30th of May 1941 under Milan Aćimović. The Government of National Salvation led by Milan Nedić replaced it on the 27th of August 1941 after a meeting of seventy-five prominent Serbs.
Einsatzgruppe Serbien executed 100 Jews and 22 communists on the 29th of July 1941 following an arson attack. By the end of that month, the number of communists and Jews shot or hanged reached 1,000.
The LXV Corps zbV commanded four occupation divisions including the 704th Infantry Division, the 714th Infantry Division, and the 717th Infantry Division. These units were raised during spring 1941 as part of the German Army's 15th Wave of conscription.