All of the previous posters have given great info about which characters to find at the Critter Breakfast.
I will add that Chip & Dale and Koda & Kenai are the most consistent characters I have seen at Storytellers. You are pretty much guaranteed to see at least one character - if not both - from those two duos if you do the character meal. Sometimes Chip & Dale are not there together, and the same thing applies to Koda and Kenai. But often times they are all there at the same time.
Chip & Dale are not rare at DLR - they can also be found at Goofy's Kitchen and at Minnie & Friends. But the Critter Breakfast is the only meal where you will find Koda and Kenai...and Terk, if it's a day when Terk is there. Meeko and Rafiki, I think, occasionally show up at Minnie & Friends breakfast. Baloo occasionally pops in to Storytellers, but he can often be found at Goofy's Kitchen.
My character sightings at the Critter Breakfast have been Koda, Kenai, Chip, Dale, Terk, Meeko - and Rafiki a long, long time ago (who may have been there with Timon, but I can't remember). I think Baloo was showing up as I was leaving one time. I also saw Pluto there back in 2001 (maybe Pluto runs through the forest and that's how he qualified to be a woodsy character?

).
I've never seen any more than 5 characters at the Critter Breakfast at one time, and sometimes only 4 characters, but I don't really hold that against them because I think that
all the character meals (with the exception of Minnie & Friends) fluctuate in the number of characters on site at any given time.
Minnie & Friends is the meal that most consistently has a lot of characters on site at one time - usually, anywhere from 8 to 14 characters!! That one has more characters than any of the other meals, as a rule.