This is sad to hear. I just finished watching the series myself and I loved it. I too wish for another season , but would understand if it does not get one. Condolences to the family, friends and fans that have lost her.
I definitely agree with Alexis Tipton playing the part of Anna. She just fits so well as that part (Saya Kisaragi from Blood-C is a good example). If I were to choose ONE person. OOOOOOOOOOONE. PERSON. To play the part of Okuma, it would probably have to be Josh Grelle as well (see Yukiteru Amano from Future Diary for reference). I agree with your choices and I really hope this gets a release and soon! Maybe with a limited edition copy? One worth the money and not that trashy "limited edition" that they did for Dragonar Academy.