You should definitely build your carreer first, with a strong emphasis on independant work and illustration. You're frankly going to have to do more than just draw cute characters in order to get a job in Japan.
First, there are more than plenty of people who are illustrators and graphic designers in Japan--- this isn't an industry where they actually need to bring in people from the outside. Second, you might not be familiar with the way that the graphics design and illustration industry works--- It's not exactly an enjoyable one--- and as a woman, don't expect to be paid equally for equal work. Third, that I know of, outside of English conversation and teaching, as well as Jobs where knowlege of English is necissary such as support, etcetera, Japan does not have persay an active role in employing foreigners in any field, again, that I know of... (Anyone please correct me...)
In the design and illustration industries, Japanese companies will hire Japanese workers first and foremost because, a) they are familiar with the language, customs, culture, keigo (polite business Japanese), and b) will work longer and harder than foreigners will work, for less pay. I know of plenty of Japanese who have worked in the art & media industries in Japan, as Japanese, and the work is not exactly a pleasant one.
If you want to live in Japan, the first step is to learn the language--- that said, you have to realise that Japan isn't exactly a welcoming country where it comes to foreign expatriots--- You'll practically need to mary your way in, in order to live there for any time more than a year or two...
Japanese is a big commitment for sometimes not much gain, before you begin learning a language you may never use, you should try to talk to as many people as possible who work in your industry--- Find out publications (like Tokion, Metropolis, etc) that are about Japan, but are as well in English--- try to fish out leads for contacts, etcetera...
I wish you good luck.