It is usually a good idea to think about having something in
addition to Japanese. e.g. a degree just in Japanese is limiting in terms of career options, compared to having a degree in something else useful with a minor in Japanese (e.g. for translating, the people who make the most usually have a scientific or law background and do things like patent translation). Best of all in terms of fluency would be doing a BA at a university where you can do a year abroad in Japan.
After all, as you point out already, there's a large Japanese population in places like Seattle, which means there's already quite a few people around who speak both English and Japanese - who may have grown up speaking both, in fact. It will be hard for you to compete with them on the grounds of language abilities alone.
How long is this Berlitz course and what exactly are they promising you over what time period?
I would suggest you do a few things:
1. Look at job-search websites etc. for your region, or pick up a Seattle newspaper and find the job section. See what sort of jobs come up asking for Japanese speakers. Do any of these sound like what you'd want as a career? If so, what are the requirements for those jobs? Do any of them require more than just language skills? Would your first degree (I'm not sure what an AA is exactly, or what the UK equivalent would be) qualify you for any of them if you also spoke Japanese, or would you need a BA or some other specific qualification?
2. Look at the universities that you'd be thinking of doing your BA at. Contact them and ask for more info about what careers their students end doing, about what sort of courses you can take alongside Japanese, about what is required/what it costs to do a year abroad if you were studying with them. Compare this to what you'll be getting through Berlitz.
3. Consider doing a BA and then applying here:
JET Programme