The Germans had three methods of laying mines: ships, subs and aircraft. The whole feasibility of the operation depends on air supremacy over the Channel.
At Dunkirk, the Germans spent a good deal of their effort bombing the troops on the beach. Their efforts there were split [And bombing sand isn't that bright]. Plus an inordinate amount of the Dunkirk bombing was done by Stukas, which performed fairly well in early German ops in the Channel when the Luftwaffe shut it down to British sea traffic. Plus, in the Channel, the Stukas would have had company, JU-88s, a whole 'nother kettle of fish, HE-111s and Dornier pencils.
The British had a lot of troops, but they were short on transport, armor, some artillery. They left it in France. Plus, the British command system lacked flexibility, as did their doctrine [tanks fight tanks, artillery supports infantry, etc]. If the Germans get ashore , as long as they have control of the air, they could fly in grunts [At Crete, not only the 22nd Air Landing Division, but one of the Mountain Divisions as well], and some air lift capacity was available as well, at least for the initial stages.
Once the Brits withdraw air from the south, the Germans have forward airfields. To paraphrase Churchill, "Never have so many owed so much to the limited fuel capacity of an ME -109". Once the Germans are flying off British airfields, that advantage is gone. And the Germans did quite well during the Battle of Britain re: fighter losses before they switched to London.
As for the Fallschirmjaeger, we're going to have to disagree on their losses in Norway and the lowlands being decimated. I believe they had quite sufficient numbers [counting 22nd Air Landing Division to spearhead the attack].
We'll also have to disagree about the German Army's reason for their plan. They knew that the Kriegsmarine: [a] Wanted a smaller A/O ,[b] did not have the transport to carry the force the Army envisaged, nor would have in 1940, and [c] could not support that large an invasion area, having insufficient surface assets for convoy and fleet actions [two 11" battlecruisers, two 11" pocket battleships, one or two 8" heavy cruisers, a couple of light cruisers and ten destroyers]. They made no effort to conform their plan to any sense of reality. There's a reason for that. They didn't want to go, but they didn't to seem like it was their fault if they didn't. Like their Fuehrer, they were "heroes on land, but cowards at sea"
All you say is true accept this was Germany 1940 not America toady.
America has got the art of logistics down to a fine point, so fine that many people do not see it as a major problem any more.
First the mine belt, it dent matter how what assets the Germans had , but how many, how fast would they be able to lay two belts and thick belts at that. And keep laying them to protect the initial invasion, follow up units and supplies
The German forces were set up tactical to fight short sharp wars, not strategic, they entered the war with a shortage of those assets deemed necessary.
The Germans had a operation strength of around 30 U-Boats, not all were at sea, and some were on anti convey duty at the time.
The Luftwaffe did not have much experience of attacking shipping.
Also a lot of navel engagements would of been at night, The Royal Navy like the Japanese trained at night as well as at day.
The Royal Navy did not lack for bravery, it would only take a few ships to break through and cause havoc, with the second wave and the supply ships.
As for the land battle, yes the British would of been fighting a static defense, but that is not a draw back if the enemy, the Germans, did not have maneuver room.
Blitzkrieg is all about not letting the enemy know where the point of attack is, in this case the German army would of been confined to a small landing zone easier to contain.
They had no or very little long range artillery.
Most of the first troops forward would be infantry, with very little amour back up it would of turned into a slogging match, with the British fighting over the very terrain they trained in, and the Germans relying on shipping for all there military needs.
The Key to victory in the end would of been logistics something the Germans lacked at that time.
Think of DDAY it was touch and go, and we had total control over the sea and the air, it was launched in June and we had whole variety of ships with heavy lift capacity. And it was on a broad enough front, To allow the maximum=m number of troops to be landed in one day
At that time the Germans had no heavy lift capacity.
Yes the Luftwaffe could fly in extra men, extra men need to be supplied, and aircraft flying in men is not aircraft flying in supplies.
Also Crete was a victory for the Germans but they suffered such a loss in men and aircraft that it put Hitler off further airborne operations.