Go for it
Firstly Singapaul - Rice Queen to Burger King - that is fantastic!!!!
With your permission I will use that , my work colleagues will love it, let alone my friends.
I went to Japan in 1993 on a whim, as I had a few days off between changing jobs, and 50K NW points to burn. I also knew that NW was pulling out of Australia.
I got a JR pass, flew into Osaka Itami, after a wonderful flight on NW J - got the bus to the railway - got my JR pass converted and went for it.
Spent the first night in Fukuoka after a wonderful train trip on the Shinkansen (bullet train), a night in capsule hotel. (not recommended)
A day trip to Ngasaki - on local trains, then Shinkansen Fukuoka to Tokyo.
A day exporing Tokyo then to Nikko and finally to Kyoto, Osaka and my 5 days in Japan was over.
Wonderful - don't do a tour, its so doable on your own and so much fun.
Before going to Japan I had no real desire to visit but loved every moment.
Adam