A few things I don't understand.
If you know korean, english, french fluently and spanish moderatly, that seems like a bright person to me.
Many language schools are geared towards teaching students (Mainly Korean and Chinese) students to enter Japanese universities, so it is very hard to find a school that only teaches "very basic courses" most if not all the ones that sponser student visas teach "extensive japanese".
Not sure of your educational backround but most want to see high school graduates, with reasonable grades. They review it, to see if you are a good student in the past etc.
As for part-time jobs, it depends on the job you get, working in a night club would certainly not usually be allowed depending on exactly what you did at the night club. Again back to what you said, you speak fluent Korean, english, french and moderate spanish, I'm sure there are 3 things right there that can get you a job much better then working in a night-club.
It would be very difficult to find someone who is Japanese to become your room mate, too many liabilities, however ifyou stayed at a guesthouse or dorm, yes there are people who are in a similar situation, but some of them have been there much longer then you have to give you tips and know the area to help you out. Not everyone at the guesthouse/hostel is going to be there new day 1 just like you are, I wouldn't worry about that part too much.
As for a language schools, not in Tokyo, but the Yasama Institute near Nagoya seems to get a lot of positive reviews, it is something you should look into.
http://www.yamasa.org/index.html
