is this stand overkill?

The yellow 2x4s are unnecessary unless you are leaving this all open. Even with no skin if you use proper joinery techniques on the rest of the stand they are not needed and are just taking up space in the bottom. Are you skinning the stand? How you skin the stand can and should provide the majority of your strength. You could easily build a bulletproof stand without any 2x4 or 2x6. If a box built out of plywood or solid wood. So many people build stands like they are building a bench (no skin on a bench). This really is not necessary unless you are building it with all removable skin or no shin. Look at a couple of professorially built wood stands. 

relethg wrote: The yellow 2x4s are unnecessary unless you are leaving this all open. Even with no skin if you use proper joinery techniques on the rest of the stand they are not needed and are just taking up space in the bottom. Are you skinning the stand? How you skin the stand can and should provide the majority of your strength. You could easily build a bulletproof stand without any 2x4 or 2x6. If a box built out of plywood or solid wood. So many people build stands like they are building a bench (no skin on a bench). This really is not necessary unless you are building it with all removable skin or no shin. Look at a couple of professorially built wood stands.

I have very basic knowledge of carpentry (but im an expert at google and youtube) and will rely on the stand to carry the weight of the tank. I do plan on skinning the stand and adding doors to the front.