For starters if I were to overbuild something, it certainly wouldn't be the first time, you should see the deer condo my buddies rib me about I built a few years ago.
So obviously on a 6 foot run, the only concern I have without evenly spaced from supports would be for that front 2x4 to bow. I eliminated some of that by adding the support for the Electrical side, which drops it down to a 44" run. So I'm using the blue supports as stress relief for the grey supports which will support the majority of the tank.
Secondly the tank is 48x24, the stand is 72x36 so the middle of the stand will bear some of the weight regardless of the top. I was planning on going either 5/8" or 3/4" ply then tiling the top of it for looks.
So when I skin the stand you will not be able to even see the top rails. I like to use magnets on all of the doors/walls so I can remove any section at any time. It's proven invaluable over the years with my metal stand so I plan to duplicate that. I simply run a wide enough trim piece off of the front to compensate for the extra thickness of the magnets plus whatever I decide to skin it with. I do plan to put the magnets in the 2x4s into pockets to make things a little more flush, but probably not on the doors as I doubt they will be thick enough.
The theory is that it doesn't look like a door, but it comes right off.
Old Stand which would have been better if I would have stayed with the wood grain for the Sump window.