From what I've seen of the Lion Guard so far, the cast looks good, more or less. We've seen a large amount of Kion and a pretty good amount of Bunga, as well a snippets of the rest of the cast. Here are my predictions:
We already know about Kion and Bunga, so I'm not going to cover them.
I think, based on what I've seen, that Ono the egret will be kind of the "naysayer" of the group. He'll serve a similar role to The Magic School Bus' Arnold or Fraggle Rock's Boober. He won't want to go on adventures with his friends, but they'll drag him along anyway. He'll also be very smart, and use large multisyllabic words (but not TOO multisyllabic, lest it confuse the audience!)
Beshte the hippo, based on what I've seen of her, will probably be "the girly one," or at least as girly as a show like this will allow. She'll be kind and sweet, and probably be interested in adding bright, shiny things to her face. She'll like being "pretty," and make this tendency known. She'll also have a sassy side, however.
Fuli the cheetah, by contrast, based on what I've seen, will be the group's tomboy. She will be abrasive, like outdoor activities, and have a fierce temper. She'll serve a similar function to The Land Before Time's Cera or Fraggle Rock's Red.
Now, I could be wrong about all of these, but remember, they're just my opinions.