I usually buy 2 transports and a CV for Germany round 1 and try to kill as much Royal Navy as possible. If I am successful in sinking the UK ships, then I have to see what England buys. If they plop a bunch of guys on London for defense, I will start building up for Barbarossa and use my Luftwaffe to keep the Royal Navy at bay. If UK tries to start rebuilding their fleet and / or puts too much on the South African IC for fighting Italy, that usually means less guys on London so I will go Sealion with 3 Transports of men and artillery plus ALL of my remaining Luftwaffe. It’s usually successful then.
One thing though, it also depends on how much Luftwaffe survived the round 1 attack on the Royal Navy. If Britain scrambles all her fighters to the different sea zones, and I have bad dice, the Luftwaffe could get mauled and I might not have enough to attempt a Sealion. In that case, I usually start building for Barbarossa while also trying to rebuild the Luftwaffe and hope that I have enough planes and subs to still keep the Royal Navy off my back.