I was tempted to send you off to do your own research, but after poking around a little, I realize that your questions fall into some difficult holes in the published record.
1. How many employees worked in Los Alamos and what did most do?
There were several thousand people living in Los Alamos at the end of the war. Most of them were support staff; technicians, clerical workers, the army, etc. I haven't come across an actual figure yet. According to Wikipedia.org, there were 130,000 people working in the entire Manhattan Engineering District across the country by that time.
2. How much later after the bomb was dropped did the world find out about Los Alamos?
Little Boy was dropped on Hiroshima on Aug 6, 1945. Chapter 12 of the Smyth Report (Atomicarchive.com), released to the public on August 12, 1945, describes Los Alamos' work in developing the atomic bombs. OTOH, the city and lab were still highly secret for many years. I have a USGS map of Bandelier National Monument in my office dated 1953 that shows White Rock, NM. but not a trace of Los Alamos.
3. Where was most of the uranium found for the bomb?
Much of the Manhattan Project uranium came from pitchblende mined in the Belgian Congo (the Democratic Republic of Congo today.) I believe most of the uranium used at that time came from Africa. The uranium mining industry in America came later.
Good luck with your project!
