This is a rewrite of this question in an attempt to reduce its scope and bring it back within the sites guidelines.
I was writing a story set in an alternative history in which Nazi Germany occupies England in World war two after successfully conducting the amphibious landings code named Sea lion. This has been covered by others before me, but after some research I suspect that my assumption of a successful amphibious assault was totally unrealistic.
Considering the specific points noted below, can anyone make a good case for how the Germans might have successfully carried out an amphibious assault on England In the September of 1940 given the forces available to them at the time? Or is it reasonable to assume that operation Sea lion was just a threat that had no realistic chance of success because of the presence of Royal Navy rather than the RAF? Assume history was as we know it up until the end of August 1940.
The massive superiority of the Royal Navy over the German Kriegsmarine.
The Royal Navy’s ability to patrol the English Channel at night almost at will and the presence of friendly agents in the invasion assembly ports making surprise all but impossible.
The very slow anticipated speed and very large size of the German invasion fleets with each transport towing two barges at 3 - 4.5 knots.
The navigational hazards in the straights of Dover such as the Verne and Royal Sovereign shoals, wrecks, minefields and strong tides and black-out.
The German intention to conduct the invasion on a moonlit night.