Hi Ace,
I am a new rider and like you, am in a training group for the Cinderella.
I also have a "knee" (i.e. had surgery on it a few years ago and there is no more cartilage) that I like to protect so that I can still get my runs in.
My group has rode on the Cinderella course (most of it) and I can give you my perspective as a "newbie."
The two "hills" referred to are not bad...do them in the easiest/easier gears and you can ride with no knee pain. They are not short and steep, but rather longer and gradual. What I find to be more surprising is the extent of the winds in Livermore on the flats...riding in a paceline definitely makes the ride easier! When it is my turn to be the lead rider, it feels like a hill a little bit.
So if you feel confident about your general fitness to ride, you should be okay! Most of the course is flat. Hopefully you will have some others to ride with to help with the windy parts.
Good luck and hope to see you there!