I'm hoping Selene doesn't join Ash just for the sake of her name sounding too much like Serena's... I know that's a shallow reason, but seriously. Unless that's not actually her name, but anyway.
As for Ash getting the regional bird, I'm partial to this. Ash always gets the bird anyway. Just as long as he doesn't get three flying types like Kalos, and the like.
Ash getting Pikipek will definitely continue a series-long tradition. After his Flying-dominated team in Kalos I hope the writers don't make his Alola team unbalanced like that again.
Also, out of the female characters we had shown so far it has been revealed that Lillie is not a Pokemon Trainer at all, so it's definitely more likely that "Selene" (placeholder name) will be confirmed as Ash's female companion for Alola.