He could've gotten Torygg's support and not have to worry about it cause then he'd practically have the High King in his pocket. Being an advisor would've been more suitable as a guide but no he wanted the power.
He would've advised Torygg to fight back, and he would have, i.e. he wouldn't sit and wait for something to be approved and would've directed an attack.
The Imperials can't do anything with the Thalmor still breathing down their necks with dagger digging
As I said that massacre was a horrible event, it happened and will probably happen in a similar fashion but different circumstances.
MetalGod is right. The stormcloak victory generates the unity necessary to defeat the Thalmor.
No it wouldn't, the Empire would be sundered and bleeding (moreso) and Skyrim would be by its lonesome the beast races and mer would be (in a way) oppressed, besides if the Thalmor come aknockin' they'd be by themselves.