Kind of got that out of order. Create the Legions, then take the war to the Altmer. Promise to leave Skyrim to the Nords. With the Emperor dead, the Empire in disarray, and legions of berserkers and dragons hounding the Altmer and Empire embroiled in civil war, it'll be easy to forge a new dynasty.
Imperials are the Altmers bitches. Stormcloaks are racist AF.
Solution is simple. Kill the Emperor, become the dragonborn, take over the Empire, and leave Skyrim to the Nords. If they step out of line, nothing a few dragons can't resolve to put them back in their place.