Bill,
Thank you for stopping by and taking the time to tell me what you think of it.
I think that a 125gal tank with everything hidden would be awesome! It may cause more problems for you though. I would suggest having the tank visible from three sides instead of four and putting a false wall on the one side so that the water overflows before going to your intake bulkhead. In a small tank like mine, skimming the surface of the water every couple of days can easily be done with a single paper towel. In your tank however, it would turn in to a major pain in the butt!
Also, it would be neat to be able to hide your exhaust bulkheads under the rockwork in the bottom of your tank but that takes some guts too.
With my tank, if the bulkhead in the bottom of the tank fails or cracks, I have 2gallons of water on the floor and am out only as much livestock as you can put in an 8" cube. If a 125gal tank drained right to the bottom, it could be
devastating. Just somethings to think about...
If I were you, I would make the tank viewable from three sides , have an overflow wall in the back, and pump your return flow through a return manifold that runs all along the top of the tank that is hidden by the trim. Or just shoot your return flow through some bulkheads that you have in the false wall... just so you don't have to drill the bottom pane of your tank.
I don't know, maybe I'm just a nano guy that's scared of big tanks now but, Murphy's Law seems to rule in this hobby

.
Good luck and I am sure that whatever you decide, it will be a sweet tank.
- Chad