Transport question!

What is the best/cheapest way to get from Narita Airport to Osaka? We were planning on taking Narita Express to Tokyo and then taking the Shinkansen from there!

And then on the day we fly back (will be from Tokyo to Narita Airport) our flight is at 8 in the morning so ideally we would like to reach there around 5/6am, is this doable and how? Are there any trains open that early or do we have to opt for cab/uber?

Thank you!