Round 1: Danzo - Kakuzu probably wins mid-high-diff.
The only problem for Kakuzu would be Baku and the Juinjutsu, but he can take one enhanced Futon and promptly retaliate with Katon and continue to use the masks even if he's paralysed. He just has to keep on overpowerin Danzo with Katon or counterbalance with Futon and wait for his immortal time to run out.
Round 2: Tsunade - Tsunade wins this one mid-high-diff imo (controversial opinion lel).
In short; Byakugo tanks any elemental jutsu thrown if she gets caught, chakra scalpel allows her to cut his threads and masks off, her punches >> Domu...
Round 3: Minato - Minato wins mid-diff.
Domu isn't active all the time and Minato is not only one of the fastest shinobi ever, he's also one of the most clever. He just needs to tag Kakuzu and wait for an opening. The masks are taken down in a similar manner or with a summonings help (which i don't see necessary).
His SM Rasengan could possibly overcome Domu, but that's only speculation.
Round 4: Hiruzen - Hiruzen should take this high-diff.
Yeah, he's got stamina/chakra problems, but i can see the old man handling this since in the end he has got the right tools to deal with this.
Like Minato he's also very clever and highly perceptive, he should identify Domu has a Doton right away. After this a simple Raiton would do the trick. It may not be easy to catch Kakuzu off guard (since Kakashi had to rely on a surprise attack), but while Hiruzen can choose which element to spit, the masks always spit the same element, this is another point where his intellect comes into play. Once the masks are taken down i don't see why should someone as skilled as him have a problem, especially since it becomes a 2v1 at that point.
Round 2: Tobirama - Tobirama mid-diff.
Similar to Minato, nothing to add here.
Round 1: Hashirama - Hashirama (w/o trying) low-diff.
Pretty obvious why >_>