[Meltdown]

Hi, I'm a nineteen year old American and I currently am a sophomore in college. This summer, some family friends my father knows through his work gave me the offer to stay with them this summer in Tokyo as they knew I was interested in traveling to Japan. I know I can get a 90 days tourist Visa (I can, right?), so I would presumably stay the full 90 days. During this time, on a tourist visa can I:

a) take part-time English classes at a language school? Or is some other visa required?
b) get any sort of part-time employment? I heard a lot of western bars/nightlife/entertainment type places hire foreign American workers. Is this possible, or would I need a work visa? If so, can I get a work visa while in Japan and have them sponsor me? If that doesn't work, can I teach part-time private English lessons or is that require a work visa as well?

Thanks for any help.