Q: How long would the full-time Japanese language course in the YWCA take to get me to the top level in Japanese?
A: "How long"? --->For me a lifetime.
Two classes a week for two years will get you the Japanese level 3 in about two years. For level 2, more "intensive" study is needed at least 4 days a week, several hours a day for one year. Level 1 for a Westerner studying at the YMCA is not a reasonable expectation---at least 2 years (more like 4 or 5). All the Western translators working for me as just as trainees with only Level 1, took 5 or more years to get to that point.
Q: I read somewhere that you have to have JLPT Lvl 1 to enroll in a Japanese university, so... if i take that language course i still have to take the JLPT up to level 1 right?
A: To enroll in a Japanese NATIONAL university (dirt cheap, or free scholorship) takes JLPT Lvl 1 to enroll although Level 2 will be accepted for a real scientist. Private universities will accept anything but they are expensive. Your best bet is transfer into Japan as grad student in a real major (not language or humanities) and live on a general research or Ed Ministry scholorship which pays more than 180,000yen/m plus housing.
Botton Line: It's easy, fun and maybe lucrative as long as you're not in not language or humanities major.