While you wait for an answer as more can certainly be added, You might want to check out this answer by a now deleted account, as well as this answer by u/kieslowskifan

Now, referring to the second part of the question, it is quite important to note that the situation of Napoleon and Hitler were vastly different and thus cannot easily be compared, and not only due to fact that the idea of 'Napoleon being defeated by Gen. Frost' is as popular as it is false. Contrary to popular opinion, Napoleon never fought during winter, as the last detachments of the Grand Army left Russian territory in the two last weeks of December (curiously, Mongols were conquering Kievan Rus throughout winter of 1239/1240 with Kiev finally falling in early December). Technicalities aside, weather surely contributed to attrition during the retreat, but Napoleon decided to withdraw in the early autumn while Germans fared pretty well for two subsequent winters and managed to hold large areas in what is now Belarus and Ukraine through the third one despite defeats at Staligrad and failed attempt to retake initiative during Operation Zitadelle. The main problem was the supply lines and food production - Napoleon's Grand Army essentially controlled two small corridors that were constantly harassed by Russians who wanted to make sure that French and their allies are unable to forage, while Germans controlled almost entire territory between Germans and the eastern frontlines. Furthermore, the logistic capabilities of the 1812 and 1941 were completely different due to the technological advances (railways, planes, ubiquitous cars, refrigeration, food preservation) that allowed for effective production and stockpiling of supplies in Germany and then its transportation to the Eastern front. What was nigh-impossible for the French in 1812, was pretty much business as usual for Germans in 1940's. Napoleon also had to cope with poor morale among the soldiers with the possible exception of Poles who treated the campaign as a opportunity to regain independence and thus were fighting for political survival. German in 1941 boasted good morale that was bolstered further by easy victories in the initial phases of the Operation Barbarossa.

Second, the goals of the French and Germans differed heavily. Napoleon was sure that decisive military victories and capture of key cities will be enough to force the Russians to surrender or at least begin the negotiations and from the strategic standpoint, Russian campaign was a victory - Grand Army achieved victory in pitched battles, managed to inflict heavy losses on the enemy and captured Smolensk and Moscow before autumn but, contrary to Napoleon's expectations, Russians continued to resist, engaging in the attrition war French were in no position to win. Hitler, on the other hand, aimed at capturing essential production centres and even more importantly, the Caucasian oil fields that would give him an edge in the Western and North African fronts. According to the Lebensraum idea, Slavic territories (Poland and, opportunities permitting, USSR up to Ural Mountains and possibly beyond) were to be conquered and physically adjoined to the German territory to be colonised by Germans after the war (so, it was a predominantly territorial conquest, not the political one, as in case of Napoleon). It was also a rather popular assumption that the USSR is a harsh dictatorship that keeps in power mainly because of the totalitarian practices and terror and thus will topple as a result of enemy military advances.

Let us elaborate a moment on the last factor. It seems that despite the political differences and often unfavourable views of Russians as a nation (partially to historical antagonisms, partially due to racial concepts that were quite popular at that era), France, Britain and also possibly also Germany considered Soviet society as quite similar to their own and expected them to react similarly. For example, they were estimating capability of Soviet military production output with an assumption that the satisfying the civilian needs will be maintained on the level comparable with one typical for Western societies and thus not taking into account the possibility that the military production will neglect civilian market almost completely with little to no social unrest and that a extreme supply shortages will not have as detrimental effect on morale among the Soviets as previously thought. It should also be noted that since early 1930's USSR was for the large part a closed state and thus ability to gain an insight into the everyday matters or internal politics no to mention the industrial potential or capability of its development was heavily limited.

Third, Hitler was pretty much sure that he will be able to achieve his objectives until the winter (or, more importantly, spring thaw) comes. It wasn't even that far-fetched as one might think, because the whole notion that attacking USSR (or generally, Russia) is a suicide move is a chiefly presentistic point of view bolstered by the fact that Germans lost in the Eastern Front (and usually omitting the effects of Lend-Lease, USA joining the war and the lack of Japan support in Siberia). In 1941 however, there opinion that USSR is unable to withstand the pressure of well-concentrated German invasion was quite widespread. Even though the potential of the USSR was widely recognised, it was not considered a second-grade military power at best. This was heavily influenced by the defeat in Polish-Bolshevik War of 1919-1920 and further corroborated by the Soviet struggles in the battle of Lake Khasan (1938) and Khalkhyn-Gol (1939) that, although resulting with ceasefire and Soviet victory respectively, further reinforced the view of Soviet Army as substandard in comparison to modern Western military forces (OKH considered the Japanese army as weaker than European ones including Red Army, and thus assumed that if Soviets suffered significant losses against roughly equal Japanese forces, they are absolutely no match for the German army). Problems experienced by Red Army during the invasion of Poland and especially during the Winter War (1940/1941) was considered as a proof of Soviet military, organisational and economical weakness by Germans and Western Allies alike. It should be noted that this calculations were not without merit and couldn't have been attributed only to the illusion of grandeur of the feeling of racial superiority. In 1941, Red Army suffered 5.5 million casualties and further 7.15 million in 1942 while losses of German land forces were 307.000 and 520.000 respectively. These losses are staggering when compared to the casualties in the Invasion of Poland, when Germans and Poles lost 17.000 and 66.000 soldiers respectively. Boris Sokolov suggests that the correspondence between Stalin and Ivan Mayski, Soviet ambassador to Great Britain allows the assumption that the former was deeply concerned about the necessity of securing Western help as the USSR alone might not be able to stop the German advances (Stalin wasn't sure whether he can relocate Siberian divisions as the threat of the Japanese invasion in the East was still a possibility).

Of course, the above arguments do not offer the answer for a most important question, to wit _why_ Hitler decided to attack USSR. There were few strategic reasons to do it. The idea of Lebensraum and resulting Generalplan Ost was pretty much alive among National Socialists and thus the idea of expansion of the Germany by annexation of all the territories up to Ural Mountains and Caucasus seemed agreeable, especially in the light of easy military victory, as suggested by the prevailing opinions of the Soviet military prowess. Furthermore, Hitler was wary of Stalin and didn't trust him, fearing that he might attack if majority of German forces engaged in conflict in North Africa, especially after several aggressive actions USSR made against neighboring territories, including Finland and Bukovina. With Romanian oil fields located close to German-Soviet border, this could spell disaster for Germans. It can also be argued that Soviet Union was the best target for the German armed forces that were heavily focused on land warfare. With invasion of England foiled and the war in North Africa hampered by British naval superiority that also made the seaborne operation against Great Britain very difficult, Hitler and other German commanders came to conclusion that victory over USSR, securing the Eastern flank and capture of priceless oil sources and Soviet industrial infrastructure and natural resources will not only be easier but might also force Great Britain into peace negotiations.

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Cecil, Robert, 'Hitler's decision to invade Russia 1941', London, 1975

Kahn, Martin, '>>Russia will assuredly be defeated<<: Anglo-American Government Assessments of Soviet War Potential before Operation Barbarossa' in: Journal of Slavic Military Studies, 25(2), 2012.

Kahn, Martin, 'From assured defeat to >>Riddle of Soviet Military Success<<: Anglo-American Government Assessments of Soviet War Potential 1941-1943' in: Journal of Slavic Military Studies, 26(3), 2013.

Sokolov, Boris, 'Таины второй мировой', Moscow, 2000.

Solonin, Mark, 'Июнь 41-го. Окончателный диагноз', Moscow, 2013.

Stahel, David, 'The Battle for Moscow', Cambridge University Press, 2015