How long will it take to become fluent?
It depends on your definition of fluent. I assume you really mean "How long will it take until I'm satisfied with my knowledge of the language", which of course varies from person to person. What exactly do you want to accomplish with this? Do you want to just be able to read your favorite authors in the original Russian? Or do you want to be able to carry conversations, watch Russian television, read everything, etc. I hate to give you estimates, since people learn at different paces, but I know if you’re asking this you just want some kind of number.
If you just want to read:
Anywhere from 3-6 years depending how quickly you learn languages, how often you learn, and how much help you have(books, radio, people, MasterRussian forums, etc.) This is only a rough estimate, though. You may be an extraordinarily skilled language learner and take only 1-2 years, or you may take longer.
If you want to be fluent in terms of being able to speak, understand, read, and write at a near-native level:
Impossible to give an estimate. Depends again on how quickly you can learn, how much help you have, etc.
I would dare say that if you never had any real contact with spoken Russian, you'd never be able to achieve a fluent level of listening comprehension and speaking. Is it a full-immersion environment? Then it would probably take you much less time than if you learned it on the side as a hobby. But it'll take you several years, at least.