Okay, here we go.
The last ones.
Watcher = Grand Eldstar. The most important Start Spirit and it watches all of the Mushroom Kingdom.
I like Dreamer as Rip Van Fish or the Subcon
http://www.mariowiki.com/Subcon_(species) . You can give Hammer Bros the Blacksmith (no where else to put Toadsworth, so). Miller can be one of the inhabitants of Twilight Town or something. Maybe Vivian? The Agent could be that Paratroopa from Paper Mario who's a mailman.
Here's an interesting idea for Shrink: Nurse Toadstool. (: The only case of amnesia in Mario is either "Rookie" which is basically Bowser with Popple, and "Mr. L", which is, well, Luigi. Amnesiac could fit there as their alterego, maybe? Vent should be Count Bleck.
The rest I have no idea how they would fit in, so good luck and good job. (: