1) The Germans probably couldn't have "taken" Britain, because the British were defending themselves just too well and America wouldn't just let Britain perish. America was propping Britain up, while the British air force proved its superiority in the air under the circumstances. And Hitler couldn't execute an invasion without clearing the air first. Hitler COULD knock Britain out of the war, however, for instance he should have captured all the British soldiers at Dunkirk, this would have been a serious blow to the island. If Hitler had maintained his position after the defeat of France, with Britain as the aggressor and thousands of British POWs in German hands (to be returned in exchange for peace and also not available to defend their motherland), it is quite possible that America (and hence Britain) could be convinced to end the war against the Germans and allow France (as a state) to perish.
2) Attacking Russia in a full-scale total war of national survival was a bad idea, no matter when. Time wouldn't have changed that. What Hitler SHOULD have done, however, was capitalized off of the Slavic peoples' hatred of Russian rule and entered victoriously as the champion of freedom against Communism. Hitler could have introduced a whole new world order in the east, basically a series of nominally independent German puppet states. Stalin, acting from the heartland of Russia, would be forced to make a peace and the Russian Empire would be dismembered forever (or at least for a while). Hitler ruined things when he enforced a policy of mass extermination in the East, which undermined efforts to build any new type of order and turned all the local peoples from fervent pro-nazis into fervent anti-nazis, creating the kind of situation that could (and did) bring the Soviet Union from the brink of defeat to victory.
Thus, by forcing both Britain and the Soviet Union into peace, Hitler could have annexed most of France and half of Russia and gotten away with it. If he and his party weren't such a bunch of racist idiots, they could have truly created a Reich to stand for a thousand years (or at least until today). If Germany had adopted a positive policy towards the Slavic peoples in the East, they could have become valuable members of the German Reich that would ensure an end to Russian hegemony in Europe forever. Meanwhile, in the west, the Germans could have fostered a new Reich that included much of France. Totalitarianism doesn't necessarily mean mass murder and racism. The German state could have remained dedicated to ideals like courage, unity, and strength without adopting a policy of mass racial extermination. Instead of hunting down Jews, Hitler should have been hunting down just communists and working on winning the support of the USA.