umm.. well learning + practice + making anything worth putting in the game from scratch or even editing an existing model = a good deal of time.
Unless you have a lot of patience and want to learn now, it might be better to take it slower and get someone to help you out with your model.
The best way to do that is to get in bed with a campaign and do some work for them and have somone make a model for you.
And you're going to have to learn to fred if you don't know how already. That'll take just as long as the modeling will. They're probably equal on level of fine art, but are at different ends of the spectrum.
From self experiance, the best way to start up your own story is to not, until you get some friends and skills. I'd start off learning to fred well and/or model and join up with a campaign. If you learn the basics of freding and can make a rudimentary mission, you can learn the rest and become better when you join up with another project.
