Just wait for others to chime in. Specifically look for people who have similar growth patterns/tendencies as yours (as opposed to people who start off with dense, distributed, even growing, thick hair)
My bet is they will give you strong encouragement.

I will point you @ Olybeard: http://jefffsbeardboard.yuku.com/topic/20923/Do-It-Yourself-beard-Olybeard-approaching-22-months?page=1#.UiDVP2bn9aQ
There are many other examples of folks who started off patchy, and went on to admirable beards. I just cannot find the links.

Overall, I think your 3 week photo looks great, and you could completely rock that style growing it out.
As far as your full beard goal, it is harder to tell at this point. My observation is that most people (myself included) have "Hollywood" skewed ideas as to what a growing beard should look like compared to how it will end up. So I don't want to see you completely abandon hope prematurely.