Welcome to the forum and success with this new venture!

Have you considered a continuous flow system, which would keep the water level in the FT from fluctuating? Also, I'd recommend some dedicated filtration, which you can add with one or two more 55 gal drums. As far as stocking rates, that's a tough question because there are so many factors that go into this. I have tilapia and have gone with a 5gal FT/fish stocking rate, which is working well thus far (started my current system in Feb 2013), but note that I have dedicated solids and bio filtration. Also, I am new to this game as well, and am only sharing my experience, not offering expert advice by any means.

I second Roger's sentiments to have patience and read some more/get more input before plowing ahead. Much better to take your time and do things right initially than to deal with the frustration of fixing problems later. There will be a learning curve regardless, but you can do a lot to minimize the growing pains.