We're thinking about trying for #3 and are finding that our preferences have changed a lot in 5 years since we last talked baby names! We have literature themes for our LOs and their names also have Greek origins. DS is Theodore Robert, named after Theodore Laurence from Little Women, nn Teddy. DD is Anastasia Josephine, mn is after Jo March, nn Annie. I'm a huge Jane Austen fan but Elizabeth is not a first name option for us. I also love the Harry Potter books. So here's my short list:
Catherine Elizabeth
Hermione Jane
We like nicknames. What are your favorites for Catherine and Hermione? Also, in the HP books the character's name is Hermione Jean. If you're a Potterhead, will you look askance if you hear Hermione Jane instead? TIA!
Re: Catherine or Hermione
I’m sorry, I don’t think I could ever get on board with Hermoine. She will be forever asked, “like in Harry Potter?”
Other HP names:
Lily
Ginny
Luna
ETA- or you could use Winnie short for Wilhelmina, Winifred, Winona, or Gwendolyn
If you like Minnie then what about Minerva (as in McGonagall)? I think it's a nice name and not as recognizable as Hermione.
ETA: I forgot to answer your questions- for Catherine, the nicknames Cat and Cathy are nice. I would just pick whichever one fits your DD the best. Hermione really doesn't have much NN potential besides Hermy which IMO isn't great. I used to read HP fan fiction and I sometimes saw people use the nickname 'Mione (just drop the HER) but I'm not sure if that's reaching. And no, I would not side eye Hermione Jane.
Molly (Weasley)
Angelina (Johnson)
Katie (Bell)
Helena (Ravenclaw)
Penelope (The Watsons)
Selina, Hannah, or Clara (Emma)
Louisa, Georgianna or Harriet (Pride and Prejudice - also how sweet is Hattie short for Harriet?)
Those are just my favorites, but there are so many great options!
Also, Hermione herself may be a tough character to live up to... OR... live down. Will your future daughter want to bear the name of a super-smart (but occasionally annoying) student?
Another consideration -- when your daughter is the right age, you will want to share your love of the books with her. Being named after Hermione might make that future reading experience weird for her.
FWIW, we named our newest cat Padfoot, and EVERYONE who hears it says, "Oh, did you get that from Harry Potter?" I can only imagine the reaction to a child named Hermione.