Well, eidolon options are restricted based on where she comes from, and she comes from your naughty little head, so I'm pretty sure that means tentacles are fair game.
I'm not a fan of those restrictions, either. They do more to limit creativity than make any sort of balance. Besides, with just one character and a pet? I'm willing to give you a lot to make things a little more fair.
Wand of CLW is never a bad idea.
The pair definitely
skews way towards the weird end. Orelia more than Asta, honestly. As one member of a larger party, it would be one thing, but solo, I'm kinda gonna be forced to swing hard one way or the other. Either it's gonna overshadow most of the game and pepper most character interactions in ways that will honestly probably get old after a while, or the Final Fantasy route of, "You walk into a bar. Apparently this weird crazy thing no one has ever seen before is a normal and accepted part of the world." If that break doesn't work for you, and you'd rather mellow out the weirdness in favor of a little more internal consistency, feel free.
Do keep in mind, if Orelia is packing full time, then that is coming up every time she gets in bed. It could totally be a sometimes thing. Maybe some sort of lesser alter self or something in place of the Darkness racial.
And for the record, many NPCs who are male in the book are totally gonna get girlified.