Kashrut and Learning

Question

A couple of questions: Can you please explain the reason why it is permitted to use one dishwasher for meat and dairy? Could you also explain why if they are accidentally washed together this is permitted? Also, why isn't the halacha different for ashkenazim? Unrelated question: What does your father recommend as the best approach to developing one's yediat hatorah. In other words, which topics and sefarim, and what seder limud, does he recommend, and what does he advise against. In particular, which acharonim does he spend time on and which does he feel are not worth investing too much energy on? Thank you!