How harsh are Japanese customs when you first arrive at the airport?

Question:

I am traveling to Japan for vacation for a period of 3 weeks. I am going to be backpacking around Tokyo and I am wondering how harsh are Japanese customs agents at the airport? I am not smuggling drugs or anything or working, however I am 19 and I am not staying at any hotels(i am staying at hostels and internet cafes). The reason I say I am not staying at any hotels is because I heard sometimes they will ask for reservations, and if they ask for some from me I wont be able to give them any because I am not staying at hotels.

I was also thinking I should dress up business casual, however I am having second thoughts as that might give the impression I am coming to Japan for work(they dont like that) when I am only coming for tourism.

Answer:

If you look clean cut and dress neatly, you won't have any problems.