Did they have the troop transports necessary to move the invasion force across the Channel, and did they have plans for how they would resupply it after the landing was made?
In addition to /u/white_light-king's comment, I would like to point out that a precondition to any variant of Operation Sea Lion was that the RAF had to be neutralized. As such, the Battle of Britain itself could be seen as part of the plan to invade the UK. As the Luftwaffe lost the aforementioned battle, the RAF was left as a credible obstacle to any invasion of the British isles.
The Germans had TWO plans for Operation Sea Lion, the invasion of Britain.
The plan prepared by the Navy and Air Force had a small 9-11 division assault on a narrow front. This plan taxed the available shipping, which consisted of river barges, to the limit, and would have failed with a bit of bad weather, let alone Royal Navy opposition. This plan was completely rejected by the Army,with Halder saying "I may as well have put the troops that have landed directly into the sausage machine"
The Army's proposal required 40 divisions to land on a broad front. There wasn't even close to enough shipping to make this happen.
These two plans were never really reconciled, although the smaller option did get slightly further in the planning stage, with barges and tugs being collected from wherever they could be found.