Kiki Aru is rather confident in his own immortality, even though Ruggedo wisely points out to King Gugu that Ozites, while they do not age to death, can be "killed," more or less.

Let us explore the idea that "nobody in Oz ever dies" for a minute. If nobody ever dies and the birth rate is above zero, overpopulation will eventually ravage the food supply and make most of the citizens hungry and miserable, as well as created and ever-increasing group of extremely enfeebled people.
This bit is fixed by the assertion earlier in the series that nobody in Oz ages, and so presumably the birth rate is very low. If nobody in Oz ever ages, I feel real sorry for the parents of Ozite infants who will never get a full night's sleep from now until eternity and the parents of surly teenagers who will never grow out of it and the seven-year-old who will never ever get a later bedtime and the young lovers who will never be of age to marry. Also, if nobody ever ages, how on earth does the school system work? Do all this kids repeat the same grade every year or are there 4-year-old with PhD's?

Ruggedo sure is a lousy schemer. Wouldn't a less complex plan be to sneak into the Emerald City as beasts, transform all of his enemies into rocks, and then usurp the empty throne?

And why is Ruggedo the goose stil afraid of eggs? Geese aren't poisoned by eggs. Only Nomes are. And after being transformed, he's no longer a Nome.

What are kalidahs doing as far North as the Magic Flower? I though they lived between the two chasms in the Yellow Brick Road in the Munchkin Forest.

Trot and Cap'n Bill are dressed for spring/summer and yet claim to be wearing wool socks.

And I sure wouldn't want to eat a cake that twelve monkeys had been sitting in!

Some Oz fans over the years have suggested that, rather than all staying at the same age they were when Oz became a fairyland, people in Oz can actually choose the age at which they want to stop aging. This theory has some support in the original series of Oz books in Ruth Plumly Thompson's "Kabumpo in Oz," in which Prince Pompadore of Pumperdink has celebrated his 18th birthday party each year for several years, but, when a distressing crisis develops at the latest one, announces that "This is the worst eighteenth birthday I've ever had! I'll never have another as long as I live!" In a later Thompson book, "The Purple Prince of Oz," this same Prince Pompadore is revealed to have become the father of the only human child whom we definitely know was born in Oz during the course of the Oz series, his daughter Princess Pujonia. The ability to choose one's age, combined with the low birth rate implied by our never hearing about any new human babies other than Pujonia, may resolve some of the dilemmas you posed, Shira.
I always presumed that, no matter what shape Ruggedo was transformed into, in reality he remained a Nome and therefore eggs were still poisonous to him.
As for the Kalidahs, perhaps Baum was simply choosing to establish that their range is larger than we had thought.