The lecturer mentioned in a previous video that if you are not 100% confident with your choice, then you are merely guessing, and that does no good on practice exams/questions. The point is to master the concept, so that when you take the LSAT you are as confident as you can be to identify the correct answer.

Yes, why would you skip the foundations? It literally goes over structuring of a sentence, grammar, and logical arguments. Unless you think you're a master in all of those topics already.