Hi, I am retaking the innovation challenge on the 7th May too! In regards to the amount of detail - do not bore the examiner. I suggest making brief notes and bullet points, as well as slightly detailed designs. Do 8-10 simple designs (this will get you in the highest mark-band) with details on manufacturing processes, materials, sustainability, measurements, ergonomics and production.
Make sure you have a lot of things in your job bag. If we all have the same scenario/pre-release then I suggest you start concocting ideas about what they should ask. In addition to this, do not stray away from your area of expertise. I did and ended up reading the entire question wrong (and failing!)
If you need any specific points then let me know - I am aiming to obtain an A in this exam. My mock that I have done recently seems to be in a top mark band too.