Hey mate. I am currently living in Tokyo and came here a bit over 3 months ago on a working holiday visa. Like Rezz was saying, no one actually moves around every 3 months, that is a little unrealistic. That sort of stuff is just written there really for the sake of it (to make immigation seem like they are doing a good job) and unless you did something kinda messed up over here you will be right living in the same place the whole time. With that said however, I reckon that if you got into trouble for something else over here, they would then use it to ream you up the ass even further.
My main advice for comming over here man is to make sure you have a healthy bank account before comming. I have blown well well over 10K since getting here just on living expences so just be aware of that.
As for work, if you have a university degree it will be a piece of cake. With a degree and 1-2 years of relevant experience I know of jobs that will pay anything between 60k-150k in the first year. You really just have to be very motivated and start knocking on doors as soon as you arrive. Do you have a degree? What kind of work experience backround do you have? What are your Japanese skills like?
In all honesty, if you don`t have a degree will be an uphill battle, but not impossible. It will reallly depend on your personality.
Actually getting back to the visa situation, if you get a (career type) job (which you will need a degree for) you wont even have to worry about the visa thing because most companies will be able to sponsor you anyway with a relevant working visa. That is what is happening with me anyway.
If you have any questions, don`t hesitate to PM me. Whether you are going to be able to survive here or not really will depend on you. Despite what a lot of people think it is a very tough environment here (in Tokyo) especially if you are chasing carreer goals and not just a good time.
Good Luck!