Rebecca,
When we did Bigger Hearts with our son, we looked at it as a year of training him to read from the guide and to do his own readings. This really helped my son be quite independent and was excellent preparation for learning how to follow written directions!
I had him do his own history readings and science readings (because CM says that a child of 9 who is able to read his/her own books should) and mine could. I had him get me when he was done reading and we did the follow-up activity together. However, before coming to get me, he was responsible for reading the directions for the activity (in the bottom left box) and getting everything ready for me as best as possible so that when I arrived, we were ready to go!

He did his timeline, art, notebooking, and vocabulary (eventually) on his own, reading right from the guide. I just checked them when he was done. He practiced his Bible verse on his own and did his Bible verse copywork on his own. He also read over any questions in the Bible study box, and thought about the answers prior to me coming to discuss with him. Then, we did the Bible Study discussion. We listened to the hymns at lunch with all of the kiddos and me singing along.
My son did Cheerful Cursive on his own, following the schedule in the guide. He often read over his English 2 lesson and was started on it by the time I joined him. We always did at least half together though, to make sure that he got it. He always began his math on his own and I would go over the textbook lesson with him after he'd looked it over.
I did formally set aside a specific time each day to teach Drawn into the Heart of Reading, as its such an important area to make sure kiddos are thinking beneath the surface of what is read and learning to read with discernment.
My son honestly did the science completely independently, with me just checking in with him to make sure he did his lab sheets correctly and seeing that he had performed the experiment correctly. I did listen to his oral narrations with the science book in hand. Sometimes, he narrated to a younger sibling (with me looking over his shoulder).
The Extension Pack readings are meant to be done independently. In a different thread, I think we visited about practicing the skills of oral narration this year quite a bit and also having him dictate a written narration for you to write down for him (and then having him copy several sentences from it).
I honestly think that having him work on his writing and spelling skills this year is a key area that really needs focus before moving into Preparing Hearts. The level of writing in Preparing Hearts continues to rise and placement in Preparing is based on the skills noted in the first page of the placement chart (which includes a good dose of writing and spelling). I fear without those skills in place that moving into Preparing would only suit him in the area of reading material and would crowd out practice of core skills needed for good writing.
These are just my thoughts, and you will certainly know best, however I wanted to give you some food for thought on the many needed skills that are woven within Bigger Hearts.
Blessings,
Carrie