Keep in mind that we don't know the Gedd population on the Yeerk homeworld, and the Yeerks have proven them to be at least passable hosts. For all we know, letting the Yeerks have their own homeworld would be equivalent to letting ten thousand or a hundred thousand or a million hosted Yeerks loose on the galaxy at once. Considering that the Yeerk Empire was grown from just a handful of Gedd-hosted Yeerks originally, I'd think that would essentially spell the end for the Andalites.
Strong possibility. Those dastardly Gedds, always threatening intergalactic empires and such!
Again, one can only speculate how a million Gedds would invite an overpowering Andalite fleet but 5 billion physically superior humans? <Meh.>