I think that with the level of technology (particularly transportation) he had access to, nothing. It's simply impossible to uphold such long supply routes with horses and carriages. Even with motorized transportation, it would take enormous amounts of gasoline, which is primarily why the Nazis couldn't handle it either. I don't think he would have had any chance of taking Russia with conventional warfare (i.e. march in, take town, move on to next town, repeat). To be successful he would have needed to occupy each major transport hub for decades, install proper infrastructure, instill (some) sense of loyalty to the French, in other words turn Russia into France bit by bit, which is (needless to say) impossible within the lifetime of one man. However I doubt that was his goal, the whole marvelously idiotic idea of the Russian Campaign was a way for a peculiar and sad little man to bust his boredom and once again restore a sense of glory and accomplishment to his gigantic ego.