Congrats! :)
My fully maxed Phoenix (with Sabine instead of Chopper) can autoplay and 3* all tiers. I like that the event shows the differences in strategy required - e.g. Sidious is more difficult for the nightsisters, Phoenix only gets a few scratches on the armor bar. Therefore, Nihilus is easier to deal with for the Nightsisters. But I have one tipp some might not have noticed: in this event, contrary to raid and arena, "Plan B" does work even when Nihilus uses his special attack. So I can just let Kanan taunt, put the buff on him, and all is well. :D
Edit: That's what I did before I had the 3 stars once, but on autoplay still sometimes Nihilus dies before killing one.