Well, ok, I accept this point, even if there are too much if. First, we actually have, for what I know, one idea of the plan of battle of the Germans against England. Second, as you mentioned, England was enjoying successes against Italians in Ethiopia and Libya. In 1940, Crete was still English and Mediterranean Sea an English Lake.

So to ask for peace when you are not losing the war it quiet difficult. The French did it few days after the fall of Paris (and attacked in the Alps by Italy), the Polish when Warsaw was in flame and attacked by the Russians.
I am not sure that a man who wanted to make peace with Germany would have been elected, and in fact was not elected. THAT is fact.
Now, like you, I don’t think the Germans Navy could have cross the Channel. Again, it yook three years and more for the allies to plan and built the invasion fleet and infrastructure. How the Panzers would have work. Remember, they need petrol. The Germans hadn’t aircraft carriers, so what about the air support which proved to be decisive in France. Almost each time the French and Germans tanks fought each others, the French won. Balance was re-established by the Stukas…

Now, if UK would have sign peace with Germany, do you really believe that wouldn’t worry Stalin, one of the biggest paranoid in the planet at this time? Do you think the Red Army wouldn’t have shot down any Germans planes which violated his air space immediately? The only reason why Stalin couldn’t believe the German attack in June 1941 was BECAUSE Hitler was still at war with the UK. He couldn’t believe that Hitler did the same mistake than the Kaiser…
So, not only the peace with England wouldn’t give more freedom with Hitler, but the Red army wouldn’t have received order not to resist the invasion, Stalin being sure it was mistake. Instead, when the Russians noticed the Armies Grouping on their borders, the Red Alert would have be put on place, Stalin would have read more carefully the report from Sorge and the Germans would have found the T34 and KV2 a little bit earlier in the process. Even if the Germans would have won the first battles, we can also imagine that the Scorch Hearth Tactic would have been applied immediately. With an early defence, with no elements of surprise, the move of the war factories to the Ural wouldn’t have been necessary, so the USSR war production would have been immediate.
At the end, the key success of Barbarossa was surprise. With peace with the UK, this element would have been lost.