It's a lot of paperwork. My friend did it, and she said she had to get proof of her relative's Japanese citizenship like Koseki, birth certificate, marriage certificate, proof of residence etc...

First timers usually always go to Kyoto, Osaka and explore Tokyo. For a completely different feel, both of culture and space, you should try to go to Okinawa or Hokkaido.

It's A LOT of paperwork, but not impossible. However, you need to prove that you can support yourself and that you're reliable so you might need a company/clients in Japan to vouch for you.

No you don't, for up to 90 days.

In addition to what everyone mentioned, watch shows about adults to get used to listening to Japanese at natural speeds and many situations. I watched a ton of Japanese dramas!

You can at local drugstores. But in my experience, the dosage is a little less than say, Tylenol

Check sites like Gurunavi or Tabelog. They usually say if it's a smokefree establishment.

Yes. You have to check the special re-entry permit box on the departure form at the airport before you depart and give it to the immigration person and show your residence card