I was 24 when I got here :P
hostels, love-hotels with random chicks or alone if it comes to it, gaijin houses, a bench, I'm used to roughing it so it's hard for me to make a good recommendation.
hostels here were a lot cleaner than in other countries I've visited, it depends on your time span
it's also relatively easy for foreigners to buy houses in Japan, so if you like to be smart with money and plan for long term then check that out
I live in Kobe, it's one of the more friendly cities towards foreigners.
It wasn't that hard for me to find a super awesome immigrations officer, 3rd try was a charm!
There's nothing intimidating about it
If you do want to start a business, keep in mind that immigrations officers often have to relocate every year or 3 years to prevent from power abuse, the guy I got had to relocate a few weeks after I got approved, to get a sense of how it works.