Would it be possible to..

[40 Fl. oz.]

Move to japan, go to school, and support myself (tuition/food/housing) by working the maximum 20 hours/week?

[vvx]

I'm sure between the realm of the impossible and unpreventable, your question's answer lies somewhere in the middle. Why not see how much tiution/food/housing costs, and see how much you can make with 20 hours/week?

[GomiGirl]

Depends what sort of work you will be doing, the salary, where you live (ie Tokyo is much more expensive than inaka), how big an apartment you have etc etc etc.

[katakori]

whatever you think is a good affordable budget, i suggest you anticipate some savings "just in case", for the first month.
there are many things that are not expected from gaijins, even though they seem perfectly normal for japanese people.

for example, the money you're "throwing away" when you rent a place for the first time (read this post on greggman's site).

(and i just discovered that in many places, every 2 or 3 years when the rent has to be renewed, you have to pay the equivalent of 2 months rent in "renewal fees"!!).

[GomiGirl]

Plus the 100yen shops can fit out your place.. so there are savings if you know where to look.