While I agree with your supposition, the operative word in your idea is "temporary". Regardless of what you do in the way of negotiation, can you really see Ulfrich actually sticking to it? Unless he's dead, there is no way. He wants Skyrim. He wants the throne and no matter what you do, he is going to resume aggressions as soon as somebody turns their back.
I say, skip it and just finish the most boring questline in the entire game and get it over with. There are so many better things to do than waste your time with that bunch of yahoos.
I would much rather deal with an angry dragon that is hell bent on
destroying the world first than deal with a civil war that can be put on Hiatus easily by a pissed off Dragonborn. Seriously, when I do that quest it's like I'm a mother or mediator trying to deal with spoiled brats.
In the Season Unending quest when you fetch Tullius and Ulfric, if you have enough persuasion skill (or not, can't remember) Ulfric begrudgingly agrees that Alduin is a huge threat and must be dealt with. "The World Eater himself..."
Furthermore, after negotiations are concluded it's mentioned that he will hold the terms like "a true Nord". I know we both hate Ulfric (well, I don't hate him. I more or less pity him for what he's gone through) but he does hold true to his terms until after you deal with Alduin. Which IS the reason for negotiations. After all, Without Dragonsreach, no dragon captured = no way to Skuldafyn. I doubt Balgruuf would very much love the idea of a dragon attacking and potentially destroying his keep while Ulfric is knocking 'politely' at his front door.
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Ahem, anyway. Bottom line, I'd say do the Main Quest first, then the Civil War.
Though to make it interesting if you have mods, for a next playthrough you should deal with the vampire crisis as some sort of backstory and have Alternate Start mod or whatever it's called. Makes it more interesting.
So Main Quest, Civil War, Dragonborn, Vampire crisis. Though some do the Dragonborn Questline last.
Honest, it's up to YOU and your character you are playing as. What would your character tackle first? An evil dragon wanting to destroy Nirn? Brothers fighting brothers? A sadistic Vampire Lord that has an obsession with the sun going out? Or an ancient priest climbing his way out of oblivion and enslaving an island? (and potentially all of Tamriel)
The choice is up to you!