It's easy to get overwhelmed when it comes to biochem. Know what's in first aid, if you need to do kaplan to understand the stuff in first aid then go ahead. If you need to read a book then do that. BUT! don't sucked into it! when you know how a pathway is regulated, how to explain the symptoms of a metabolic or genetic disease, then you know that you've mastered that concept.
This is my personal opinion...we're probably not going to see a question on biochem unless its linked to pathology or pharmacology in some way. i.e. they'd give you vignette of a patient with Hers disease and ask you something about the deficient enzyme, the pathway or mutation, or someone with familial hypercholestrolemia, why would you prescribe a certain drug over the other? But that's just my opinion and that's the way I'm going about biochem and genetics
All the best