First, I basically agree with your room dimensions except that you might change the length to between 32 and 36 feet, to reduce standing waves in the ultra deep frequencies.
Second, put in as many dedicated lines as you can afford. My sound system has twelve dedicated 120 volt lines and two 240 volt dedicated lines for the stereo alone. Lighting and outlets are additional and separate from those. Be prepared to fight with the electrician on this, he will say it is totally unnecessary.
Many US amplifiers may be configured to run on 240 volt, and generally perform better ( fewer step up windings in the transformer, and half the amp draw for the same power ).
Consider using at least two, possibly three layers of five eights inch sheetrock on ALL the walls and ceilings in the room, and use liquid nails or silicone between each layer to eliminate flexing.
If possible, box the floor and walls into 18 inch squares in the framing process. This is also referred to as fire blocking. This almost completely eliminates flexing and will improve bandwidth and imaging.
Use liquid nails when installing the floor, and if pier and beam, use MicroLam beams, which are laminated (man made) beams that are epoxy pressure formed wood. Frame the MicroLam with galvanized brackets, in addition to the toe nailing with the nail gun, using plastic coated nails.
The best floor (under your proposed hard wood) is called sturdy floor. It is tongue and groove, and measures one and a half inch thick, is laminated (epoxy bound) and should be attached with liquid nails and deck screws to the Micro Lam during construction.
This will form a foundation that will not flex, squeak or vibrate, regardless of weight, placement or SPL produced by your system.
Put all the analog (or digital if your not an analog guy) on the high side of the electrical system. You can meter the two feeds from the power company, and determine the high side. Run the rest of the house on the low side, and separate the grounds between the two. I had a 200 amp (Square D) electrical panel divided into two sides, high and low. The stereo was all on one side in a solid row, and labeled. The rest of the house on the other side.
If you live were you can demand three phase, get it. Run your air conditioner (and / or swim pool equip.) on it. It will reduce your electrical bill and further remove noise from entering the stereo system.
If you can order a large "pass through" electric meter, DO SO. This type meter does not run the electrical feed through the metering equip (the meter read by the electric co.). Instead, there are solid copper bars that pass through the meter (same as your drop) and the electric companies meter is an Amprobe design. That is, it reads by "clipping" around the copper rods, rather than breaking the circuit!
You may have to fight for this type meter, and it is usually only in larger sizes. Mine is a 750 Amp. The utility is required to provide this upon request, provided you state that you intend to up your usage to require this at a later date. This may require meeting with a supervisor from the utility. It is usually a long wait on the phone, but in the end, is a FREE upgrade if they agree.
Separate grounds may be accomplished by using plastic AC outlet boxes, and running separate THHN ground to cold water pipe or copper ground rod. The rest of the house goes to the panel ground on the master box. If you are one that is concerned with ground potential, you may run a separate eight gauge ground from the panel ground, back to the same cold water pipe.
If you use metal screen under the wood floor and float the foundation (either pier and beam or slab) run a solid copper ground wire completely across the room, corner to corner, and attach to a ground rod before the concrete pour is done. This will form and RF cage, removing much of the received radio and microwave transmission that bombards our homes every day.
Do not install dimmers in the room.
Plan on spending some money on area rugs so you are not exposed to 100% hard wood floor.
Avoid any glass or doors on the walls behind the speakers and the walls immediately beside them.
Design the room with channels under the floor. PVC pipe is cheap, and may be purchased in every size. Place them between the equipment and speaker ends of the room before the pour. After construction, you have access to pull any size or brand of wire between your front end and mono amplifiers behind the speakers.
Fill ALL the walls, REGARDLESS if interior or exterior, with Owens Corning sound proof and basement R11 Fiberglass before installing the sheet rock.
I built a floor to ceiling bookcase in my listening room that attached to the foundation and roof structure. Within this space, I use solid Maple butcher block shelves two inches thick, and mount them with KV shelf bracket hardware.
This arrangement allows placement of stereo equipment where it is the most convenient and attractive, while providing adjustability for future upgrades incompatible with fixed spacing. This shelf has outlasted a dozen equipment changes, and saved thousands of dollars in (not) replacing racks and stands!
I have other suggestions, as I am currently doing this to my own living room. I know this all sounds a bit over the top, but I assure you that everything added together will not add as much to the price of your home as the price tag of a decent mid line amp.
In the end, these room improvements will have a decidedly larger effect on your listening pleasure, without becoming obsolete or requiring audiophile upgrades.
Later on, much of this would be difficult, if not impossible to implement at any price. Best luck.
