If you want the 4x4 connectors (which look way better IMHO), I bet your local Home Depot can special order the part for you. They can almost always do that — just go to their special order service desk.
Also, weight will not be an issue with a 10 gallon however you do it. The top I made with the cross beams under is is incredibly strong, and 2x4 legs would be no problem — 100 pounds is nothing to it.
Regarding size, 14" depth is the absolute minimum you can make this stand because of the size of the brackets. Look at my pictures and you'll see the brackets are about 1/16" from touching. That's with 14" depth.
Thanks mate! I agree that the 4x4 look will be much better than the 2x4 but I was curious how the other would turn out. The price seems to be the same for the bracket part but the 4x4 would be more expensive than the 2x4 but I think the look is best. I just need to find a cheaper 4x4 as I plan to paint the stand black so no sense spending more on a nice grained wood (western red cedar) if I am not staining it. I am new to all of this though so I am not even sure if I can find a cheaper 4x4!??
For some reason I am always worried that the stand won't be able to hold a 10 gallon tank. I shouldn't be when I see how cheaply made a lot of the LFS stands are and what they hold.