I think with his dogs,clones,hiding like a mole and his sesnes he can handle the mist.
Kakashi can also use a beast runner right of the bat.
The dogs require Zabuza having Kakashi's scent on him, which requires drawing blood, and again, I'm not sure Kakashi can afford to let that happen here.
Sure, I guess, though you've got distance at 40 meters. Zabuza should for all intents and purposes be able to avoid it or counter in that distance.
Clone feints would give Kakashi the opportunity to gain intel on Hidans fighting style and immortality, not on the ritual, but it takes some time to preform the ceremony.
Beast runner or water dragon will push hidan to the ground where clones would fragment him with raiton kunais.
I covered the clone feint part in my post above. Again, you're acting off the basis here that Hidan isn't going to be fighting back. Hidan's got some pretty impressive reflexes/reactions himself.
If Kakashi traps Hidan, shoves raikiri through his heart and thinks he's won, Hidan's got him just about right where he wants him. No intel is just ridiculous in fighting Hidan.
They are pretty equal, but Kakashi is able to do clones, which gives him the advantage in my opinion.
Asuma may fall for a raiton clone feint
Nothing to really argue about here.
why he doesn't win against old hiruzen, but against jiraya he does ?
Hiruzen's stamina was upgraded in part 2, Meaning he's able to create 5 shadow clones and use all elements at once. I know edo's chakra replenishes, but it's not unlimited. Meaning his chakra reserves are no more than what he had alive, it would just replenish after being used, so his base chakra reserves are enough to pull that off, and the ET just replenished the chakra he used.
Kakashi only has the ability to use 3 elements(well, according to DB he has the ability to use all 5, but he's not used the other two in the manga), so Hiruzen can counter each one, Enma gives him the upper hand in CQC, Enma protects him from things like lightning beast, etc.
Where as Jiraiya has only shown Katon and Doton in the manga, which Kakashi hard counters with suiton and raiton. Jiraiya would be difficult because of his versatility, but with Kakashi's ability to counter everything in his arsenal, it's a bad match-up for JMan.