Sorry it took so long
Well, These are pics of the basic setup, without metal braces. Those are just metal pieces in the shape of a "T" and an "L" at HD
building section. I think they're made by Thompson or something. You don't really need it, but they're only a couple bucks each.
For your tank, I would go with (6) 4x4 posts (one on each corner and two in the middle) with the top brace as (2) 2x4's doubled up like a vertical sandwich. Just like in my pics, but doubled. It is paramount to make sure that the fit of the vertical post to the horizontal beam is TIGHT... not break-the-wood tight, but tight enough that is snug enough to be coaxed in by a hammer. As the stand will naturally sag (and most, if not all do) the entire weight will be taken by the posts, and not the stand.
The only thing that I didn't add was a 2x4 that connected the front set of supports to the back end... but it's not really needed as it holds no weight. You may want to consider adding one from point A to point B and just secure it with a simple 90 degree corner bracket. I'll see if I can go on a hardware sight and get pics of the metal themselves. For now, you can build the entire thing, and reinforce later with brackets (as they hold no weight, they're just for support to make sure the top doesn't slide anywhere off the vertical posts)
Just for reference, the "L" shaped metal piece will go at the (4) identical point C's, and the two "T" brackets will obviously go on the middle two supports.