Edward died in early January, and mounting an invasion in winter, specially if one has to cross the English Channel, was not advisable. Besides, invasions take time to assemble, even if you do not have to provision them because you expect to find food once you enter the new country. It was also important to William to gain moral support in the form of a papal blessing. William of Poitiers claimed that Pope Alexander's consent came along with a papal banner that could be carried by the army; however, Alexander's consent seems to have come after the conquest was complete. William of Poitiers also claimed that the duke had support from Holy Roman Emperor Henry IV (not likely, since Henry was still only 15), and King Sweyn II of Denmark (also unlikely, since Denmark had problems with Norway and Harold of England was an ally of Denmark's in that regard).
William had months to bring together troops from Normandy, France, Brittany, and Flanders. They were all instructed to gather at Saint-Valery-sur-Somme, a seaport on the River Somme estuary. (Joan of Arc was held there before being taken to Rouen to be burned.) The summer months also included a ship-building campaign.
His numbers of men and ships was likely exaggerated by contemporary chroniclers, but for the sake of argument, let's relate that he was said to have 726 ships (including one paid for and outfitted by his wife, Matilda). Those same writers also claim different numbers for soldiers, as high as 150,000; also, as low as 14,000. Modern estimates reduce those numbers to maybe 7000-8000 men, of whom 1000 or more were cavalry. The others were archers and foot soldiers.
All his pieces were in place by August, but he delayed the crossing. The assumption is that Harold knew William was planning an invasion and hd troops all along the coast. There would be no surprise attack.
Help for William came from an unlikely source: Harald Hardrada, King of Norway. No, Harald was not an ally of William's or offering support. Harald wanted England for himself, so he attacked in the north, drawing King Harold Godwinson's troops away from the south.
For details on how that went, come back tomorrow.