I don't know whether you're on a first time visit or are a regular, so apologies if some of this is obvious.
Not been to Wa Yamamura, but I can recommend Sushi Yoshitake as a truly lifechanging meal in Tokyo (Google is telling me it's $300 which is cheaper than its sister restaurant Sushi Shikon in Hong Kong. ).
I'd also like to point out the extreme unlikelihood of anything from here causing anyone a stomach upset. It's almost inconceivable (unless you have allergies I suppose). Chef Yoshitake has a personal relationship with his suppliers over many years and the quality and freshness of the ingredients is essentially what this place is all about. It's not about fancy plating or chandeliers.
You can't book most Japanese restaurants a year in advance. They usually seem to have a policy where booking for the month after next begins at the beginning of this month (i.e. 2-3 month window). Being quick on the button when new space is made available has been as successful for me as using Amex concierge.
Most M* restaurants are accessible for English speakers and so are hotel places but some of the tastiest food I had there was in places that weren't M* but you needed a Japanese host (you would probably call them mid-range, they are never going to stand out from their peers enough to merit a star). Many other places you can also get very tasty food by having some brass neck and pointing at things, but some unfortunately you can only visit with a Japanese host even if you speak perfect Japanese (which I don't by the way). That goes from the best cheap Ramen shops to the high class eating clubs (which your host probably wouldn't take you to anyway).