We highly recommend you this! But even if you can only answer three questions with difficulty, this is a very important and valuable experience for you. This means that you have encountered a gap in your previous view which, at the moment, you do not have an answer to. This problem may be healed by research or reflection, but perhaps not.
If you do not find a solution to a specific question, it depends on the question whether you trust to find the answer later. This can be the case, for example, in question 6, the question how you intend to make money with your business idea. In business practice, you often need several attempts to find the right revenue model. For other questions, you should not rely on the fact that the right answer is given to you "sometime in the future". This applies, for example, to the question of exact ideas about your future customers.
We advise you to give each of the Seven Key Questions at least one try to answer them with your current knowledge. In later processing cycles you will inevitably come back to the only obscurely recognized weak points and gradually improve your view of things.