We will be visiting the lounge roughly 4am to 9am - arriving NRT and then leaving to VIE. This is 'breakfast' time - the menu doesn't look particularly inspiring for breakfast.
I assume other than the breakfast options listed, they also have some buffet options?
Yes, there is a buffet. While the a la carte menu is not large, I found the food quality a few steps above most business class lounges on other airlines. I've eaten from both the breakfast and lunch / dinner menu having spent a total of roughly 16 hours in the garden lounge this month.
There is also a deli area right before the dining area in the Garden lounge that has a different a la carte menu.