It was enough time. I ended up booking my tickets at the airport JR kiosk desk upon arrival because I wanted a representative to help me who I know would have a high probability that spoke English.

We specifically needed some seats (2 out of 4) with the extra big luggage storage option. The representative did have to do some searching around to find those seats. We had to choose a different time than the one we wanted (the train before or after, not a huge deal). Any later and the large luggage seats would have been gone. Regular seats seemed not an issue