I had thought long and hard about those overflows. It sucks monster balls to need to have them internal, but it was part of the trade off process that got me the longest tank possible. The tank is flanked on either side by 2X6 studs, which support walls one either side, like in this pic:
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I had them use 2X6 boards instead of 2X4 boards to give me extra depth in the stud cavities, but then as the house construction process went on, we ended up needing to put more and more stuff in to those walls. It's kind of hard to tell cuz they've already started painting, but here's the stud spaces:
North side:
One of the two stud spaces is blocked off so a bank of switches for the opposite wall could be installed (I fought this, but there was no where else to put them). Those switches will eventually be completely sealed in from the tank space. I had them position the switches so there will still be enough space above them for an MP40/60 motor
South side:
From left to right there's a partial stud space that had to be sealed as it's part of the cold air return system from upstairs, drain and water lines (that get way busier under the tank) for the aquarium and R/O unit, and a drain line for a bathroom that's on the floor above the tank.
At best, having external overflows would have made the stud spaces too crowded to work in them, at worst, I would have had to reduce the length of the tank significantly to get them in.
I would say the biggest 'theme' of this tank so far has been compromise. I'm asking it to be viewable on both sides, while being as large as physically possible in the space, and to do things that would normally require a whole fish room (automated water changes and such), but with only the space of the cabinet to work with. It will be interesting to see if it all works out as planned...
As for the lights, I think I'm going to put them in 2 rows of 3, but probably not evenly spaced. I'm thinking I'm going to do three 'islands' for the aquascaping, so I'll focus the pairs of lights on to those islands. We still haven't worked out what the lights are going to hang from, I'm thinking some sort of frame that hangs from the ceiling that I can raise and lower as one unit, but I would also like to be able to adjust the position of individual light fixtures on that frame.