Hi and welcome to the forum. While I don't have any direct experience with moving to Japan, I have moved around internationally quite a bit, and I have a friend who just moved to Japan last year.

Basically, the big problem with your plan is that if you go over on a temporary visitor's visa, you can't just keep renewing it. To stay for a longer term in Japan (or most other countries) you need to have a "long stay visa" - one that will allow you to actually take up residence there. And that normally requires you to have a job offer or some other reason or project to be in Japan for a specified period of time.

The Japanese embassy has a handy chart that outlines the various types of visas they offer: MOFA: A Guide to Japanese Visas - Types and Categories of Visa

According to my friend (British) who has recently moved there, they seem to be quite strict about the requirements for visas. It's possible to get around some of the more onerous requirements if you have a large employer backing you, but otherwise you must apply for your visa from outside Japan and have your job lined up before you apply.

It's probably not a bad idea to make an initial exploratory trip as a tourist first to see how you like the country - and to look around a bit to see what the job market over there is really like.
Cheers,
Bev