I agree with @locationunknown, you should ask your future users.
Given your description, I am wondering what you want the recommendations to be based upon: simple frequency of prior use will not really help, as you seem to have different topics and different levels of expertise in your set. So the first question with (B) is how you want to bootstrap the recommendations (user profile, last few questions taken, etc.).
The main difference that I see between (A) and (B) is where the initiative is coming from: (A) requires the user to search/filter/explore, while (B) requires the system to present proposals. As we don't know anything about your users (their motivation, their proficiency, their frequency of use), it's hard to choose between these two fundamental options.
That's also the reason why the question in (C) does not make much sense, I believe: If you support both ways of access, the proportion of (A) vs (B) is determined by how often the user will take the lead and search for something, instead of clicking one of the recommendations. You (as designer or system) cannot really define that proportion.