Is this amount of play okay? 2007 Prius, very small transmission fluid from passenger side CV axle.

The leaking seal is actually a pretty common thing on the Prius. I've done it 2 different cars. You might want to drain and fill the fluid again when you're done.

 

I don't know the exact number, but my understanding is there is some amount of play allowed. Any chance you know someone with similar Prius so you can check what they got?