The Treaty of Versailles was way too harsh. Hitler never would've been able to come into power without it because he wouldn't have had any leverage. And, and: England barely won the battle of Britain. Part of it was dumb luck and the other half was your accents better flying, I suppose. Really, it would've been stupid for the nazis to try to invade England by conventional means. The British navy commanded the waters of the channel and even hitler knew it. The only reasonable way to go was to attack from the air, because the Luftwaffe had, in theory (as well as statistically), a serious advantage over the RAF.
The Soviets were actually using Germany to crush the pro-democracy movements in Poland (among other places) so that they could invade and capture the country without resistance (because communists are so much better than nazis -_-). Besides, Hitler and Stalin were both egotistical and each thought he was better than the other. An attack was inevitable... the only questions was when and who will strike first.
Winter was by no means anyone's ally. During the battle over Leningrad, the city was fought over building by building. Both sides were practically starving and could snap off their own fingers and toes due to frostbite. If you found a coat on or extra socks or anything, you kept them! Sure, some of the Russians were probably more accustomed to the cold temperatures, but there was no significant advantage. Besides, Russia had the most overall casualties in the war (because they didn't train their armies well and were an insult to everyone else >__>).
If they had stopped at the Russian border and taken the war south to the Arabian peninsula and captured a territory that could provide them with more oil and fuel, they could've lasted a lot longer. If that had happened, than the new tech and weapons that they were developing during the end of the war could have actually been implemented (idk if that's the right word). We would've seen missiles that could've hit the US, flying-wing style aircraft, faster and more maneuverable heavy bombers, more efficient tanks, etc. I don't think they could beat the USA and Russia (with the a-bomb and all), but the war could've been a lot longer and much bloodier. And, more innocent people would've died because of Eichman and Hitler's "plans".
[see above for my thoughts on this... it's all mixed together]
I'm on "holiday", so it doesn't matter.