Here’s one suggestion you might want to consider. Before you focus on the finer details of the game mechanics, you might want to pull back and look at the broad elements of your overall scenario, to make sure that: a) the scenario is sound and credible, and b) that no major considerations have been overlooked. As a reference point, start by looking at the planning and preparations that went into the Overlord cross-Channel invasion in June 1944, then use that information as a template to figure out what kind of planning and preparations the Germans would have needed to carry out to pull off a successful Sealion.
Britain and the U.S. were both world-class naval powers who were used to thinking in naval terms (both strategically, operationally and tactically) and who had vast numbers of ships at their disposal – yet it took them two years to plan Overlord and to build up the required infrastructure for it. The factors they had to consider ranged from very broad ones (the choice of the overall landing areas; the establishment of air superiority over France), to intermediate-level mechanics (planning the order in which the paratroops planes would depart from multiple airfields and the routes they would take to and from France; creating the PLUTO pipeline to convey fuel across the Channel to support the invasion forces until a port could be captured) to very small technical details (like providing US paratroops with clickers to recognize each other in the dark after landing in enemy territory).
Germany, by contrast, approached Sealion in 1940 in a spirit of hazy improvisation. Germany wss traditionally a land power, and it made the mistake of treating Sealion as basically just a large-scale river-crossing operation. The Wehrmacht was very skilled at river crossings…but the point is that the English Channel is not a river. It’s much wider, and it sometimes experiences severe weather conditions unlike anything found on a Continental river.
The good thing about your scenario is that it’s set in 1942, not 1940, which means that Germany will have had about two years (since the fall of France) to plan and prepare it. So in working out your scenario, you should start by figuring out the broad-level strategic and operational requirements Germany would have had to meet to pull off a succesful Sealion, and to determine how Germany would have spent the period from 1940 to 1942 refining these plans and creating the infrastructure for this operation. Answering these questions will tell you what elements will need to be in place at the start of your actual game, what objectives Germany will have, and thus what counter-objectives the Anglo-Americans will need to have in order to defeat the invasion. Essentially, the Sealion in your game should be an operation that Germany has planned and prepared for two years, rather than a semi-spontaneous operation improvised as the result of an Italian suggestion.
