Short answers, pulled from the story.
The fall of Singapore occurred on the 15th of February 1942. This event exposed weak forces in Malaya to attack and allowed Japanese forces to advance toward Ceylon.
Admiral Chūichi Nagumo commanded a core of five aircraft carriers including Akagi, Sōryū, Hiryū, Shōkaku, and Zuikaku. Carrier Division 5 contained Akagi, Sōryū, and Hiryū while Carrier Division 2 contained Shōkaku and Zuikaku.
Squadron Leader Leonard Birchall spotted Nagumo's fleet at about 16:00 on the 4th of April. His PBY Catalina flying boat transmitted the sighting before being shot down by enemy fire.
Vice Admiral Jisaburō Ozawa's Malay Force sank 23 merchant ships totaling over 130,000 gross registered tons in three days. This occurred as part of the initial phase of Operation C targeting Allied shipping routes.
The target date for the attack on Colombo was set as the 5th of April. Japanese forces departed from Staring Bay, Celebes, on the 26th of March to execute this plan.