Hm. I've never taken a course and didn't spend all that much time studying and I can read many VNs without using a dictionary and most without using a dictionary much. Although I guess the way I read VNs before I got to this level probably counts as studying - I extracted the text and used JDICT's text glossing or Rikaichan to read all the words I didn't know. I started about 9 years ago, but didn't use Japanese all that much until about 5 years ago. I figured it would take a lot less time if one were to actually sit down and study a lot. I think the only part that may actually be hard is getting an idea for how Japanese grammar works. Once you've gotten past that, the rest is just increasing the amount of words and grammar you know and getting more practice. If you use something like Tae Kim's Japanese Grammar Guide and spend 10 hours a week for a few months on just that, you should be able to understand and memorize at least most of it. Take another two to three months to acquire a very basic amount of vocabulary and you can start reading VNs using a dictionary. Then it's just a matter of how much time you spend reading.