Unfortunately, "les jeux sont faits." I've already booked a non-refundable rate at the Hilton NRT for the first night.

I should have checked with the experts here before doing so, but in another thread, someone mentioned that the Hilton NRT offers a cheap alternative on the first night when all one needs to do is check in and sleep and then depart early the next morning for business in Tokyo.

Based on my jetlag experience when visiting Hong Kong last year, I will be up by 4:00am the first few mornings. Therefore, after an early breakfast, I can be "on the road" to Tokyo and be at the Conrad by 10:00am. Otherwise, I would be sitting in the hotel room waiting for things to happen/open.

So, I deduce that the answer to Question 1 is that I do have to go back to the airport to take the N'Ex and that I won't be able to use the ticket from the Narita train station.

In the future, I will definitely check here first before booking anything non-refundable. Again, thanks to all for your helpful advice.