You could have provided more detail. I've asked pen pals some details about it out of curiosity since I know immigrating to Japan is hard. So japan gaf could give you a better answer than mine.
Anyway, do you have a degree(engineering, programming, or anything for teaching English) or a job line up? I would say no the to latter since this seems like this is a random action you want to take. Getting an apartment might be hard since you need a guarantor. Most landlords, if you don't have a guarantor, will not let you rent an apartment out. Thus guest houses are ideal(I think). My penpal went into more detail but I don't feel like pulling out the email at this moment so what I wrote about the guarantor is based on memory. Of course, I didn't even bring up numerous of other things like a visa.
Also, why Japan? Do you want to just live there to study? Live there permanently? This will be hard to do without a job lined up. Jet program might be what you want if you want to live there a year, get bored, and then move to a new country. Also, you don't have to know Japanese for that.