Glad I found your new thread early. Here are all of my thoughts, which you can go with or disregard as you see fit.
<b>Circulation:</b> I hate anything in my tank, which is why I use the VorTech pumps. You know that -- I don't want to see Tunze Waveboxes either. Jar*Head apparently suggested the same thing I'm thinking, two external boxes flanking the overflow box at one end. Insert each Wavebox in there and press the pump through the hole so you don't see anything from the front or the end. If the plan changes some day, you can close and seal those holes with a bulkhead and threaded plug, and then have two dry boxes - maybe to put the motor side of VorTech pumps, for example. The boxes won't affect the look of your tank even if they are empty. You could even toss wet nets, sponges and scrapers inside, always within reach / to drip dry.
If the tank is too thick for the VorTechs, you might see if the guys at EcoTech could create yours specifically for the thicker tank. Since it is a glass tank, there's nothing to worry about other than the strength of the magnet. These could be placed along the back wall to create some cross flow (in various random modes) against your closed loop pattern. That would provide constant change while not being an eye sore. Wavy Seas are fine as they are out of sight, but again you have a pump visible if you have a Tunze spinning back and forth. With your modern look and the style of your tank, hiding pumps would be my choice. External boxes glued to the tank to hide Tunze pumps would be my choice. I'm not anti Tunze, just anti pumps in general.
Lighting: You have plenty of choices. Luminarcs are fine and with such a wide tank, you'll want the huge ones. I'm currently using the LuminBrites which I think would work well too. The Minis are just too small for a tank that is 48" front to back, even with T5 lighting. With the LuminBrites, you can lift them way up (16 to 18" off the water), and still get a good spread with those 400 watters. The T5 bulbs will fill in the rest. If you have the MH up high, you may only need to move the T5 rack out to get more room to play.
Ventilation: The home A/C system should not be pumped into that room. That air can definitely flow backwards through the ductwork, drawing moist salty air into your central system which will cause damage to the coils and mold in the ductwork. Rather, having vent fans sucking hot air out will draw in cool air from the rest of the home.
If you plan to have a separate system just for this room or this room and a garage, that's different.
If you want a dehumidifier in the room, have it built into one wall so it doesn't take up space. The drain should pour into your utility sink or nearby drain so you don't have to constantly drain the small pan full of water in the unit.
The vent fans are rated in Sones. The lower the number, the less you hear. Mine is silent (1.0 Sones), unless my ear is 1" from the grilled intake. I love it. Your room and huge tank may require two or three of them, but that's better than listening to a loud one with better CFM movement, imho. You can hook them up to a humidistat if you like. I have not with mine, and it runs all the time. I did turn mine off at night during the winter months because the fishroom got so cold the heaters were running all night to keep the tank at my set point. The vent fans should push the air out of your house, not just into the attic area, or you may end up with mold issues.
If the room has any windows at all, that will allow you to open it and a door to provide some fresh air to your tank on occasion. Or you might set up a different type of vent to draw in fresh air from outside, piping that into the fishroom. It could be on a timer, perhaps.
Chiller: The chiller will probably need to be 1 HP, as I was told I needed a 1/2 HP for my 330g of water. Perhaps the chiller and the dehumidifier could both be in a cubby or closet, with a vent fan to suck the heat out that both will give off. I just spent some time talking with TECO at MAX over the weekend. They are based in Dallas, so I plan to learn more about their product line. Maybe they have the perfect one for your tank.
Flooring: Slightly sloped would be best to get that water to channel toward the drain. Standing puddles will drive you crazy. Even if you have some type of slits in an appealing pattern that the water gravitates into and to the drain would be good.
The finish can have a sandy grain added to give you traction, something valuable in a wet area. Sealing the floor will prevent its decay as saltwater is a corrosive. My old return pump used to drip in one spot, never enough to bother me. I put a towel there to catch the drips instead of fixing it, and ignored it forever. One day I was down there working on the pump and plumbing, resolving the drip. The concrete in that patch is brittle, flaking, and sounds a tad hollow when I tap on it lightly.
A walkboard that you can access to work in your tank from behind would be nice. Remember the tank Fudge has? That would be perfect! Have it built with permanent steps to get up there. It would let you reach your lighting easily too.
Walls: Plywood everywhere sounds great. A work space to do water tests under a 6500K bulb would be nice. A sink to wash your skimmer out would be great. A spot to place your saltwater mixing container would be ideal, as it would be near the same temperature and pH as the tank itself.
Electrical: Perfect! GFCI circuits and at least one standard non-GFCI (for the main return pump) would be my suggestion. Wire the room for computer access so you can tie your tank into your internet access and check on your tank remotely. If you add a phone line in there, you can take calls or even use it to maybe have a gizmo call your cellphone if the tank has a problem.
I don't know how the speakers will hold up in there, but I like it. I guess you could buy an extra one or two as backups.
