No, it doesn't get sick or spoilt if you feed it tons of candy (I tried it, hehe), just that the bat will come more often, but if you scream/tap the side of the Angelgotchi with the keychain, it will go away.
Then, when you have Maruten, if you keep it at low AP, you will get Takoten, and if you keep it a high AP, you will get Kodoten.
Then, from Kodoten, if you have low AP, you get Ginjirotenshii. If you keep it at high AP, you get Kuriten.
From Takoten:
if your AP is 0 - 20 you get Ojayitenshii (=> Unchi-Kun // Otonoten)
if your AP is 20 - 40 you get Taraten (=> Sabotenshii/Smiling Angel)
if your AP is 40 - 60 you get Pukuten (=> Futagotenshii)
This is approximate, for it may vary, but I think this is more or less how I got the different angels on mine.