I’m 29, never left the country. My bucket list is visiting Japan at the very top. I have no idea what you do or if you have to go through travel agencies, how much money you should bring etc
You’ll come across good and bad wherever you travel. When we travelled in Japan a few years ago we found pretty much everyone we dealt with was friendly and helpful. We didn’t speak any Japanese.
I wouldn’t bother renting a car unless you’ve got a specific plan for it - their public transit is excellent and will still take you out into the countryside if you want.