Well, unlike microsoft, we do not have the millions of dolars and thousands of employees to supply hundreds of animations for each animal.
However, I think, on average, the animals should have the walk, sit down, lie down, eat, and a few idle animations.
There should be atleast two animations for each phase- sitting, standing and lying down. atleast two of these six should display agravation.
usually that's enough to make it look good. Running is also nesicary. I myself am doing more on my current project, but this is on average what I think will make it look good.
Making original animals takes a lot of work- but they're definately more apreciated than the recolors, which take relatively no skill.
it's even more impresive when the animals have unique sounds. Basically, the more work you put inot hte project, the more people are going to like it.
Make something that you will enjoy working on. that will make it seem less tedious.