Building a New Listening Room on a Budget

Think about what things are easy to do now but would be extremely difficult later after the room is constructed.  Not all of these things are way expensive.  You can always buy new gear later but if you are going to stay awhile there will probably be some useful suggestions by the folks here on what you can do to the room now that will provide flexibility for the future.

• Insulation in the walls, ceiling (what is above?), type/thickness of drywall used - not making recommendations just pointing out this stuff would be difficult/impractical to handle later
• Cable routing - consider where your electronics will be located and where your speakers will be located and then decide whether it is ok to have wires on the floor or whether you want to build some sort of internal routing.  For example if you plan to have HT speakers in the ceiling, or in the back corners of the room, now is the time to run those wires.  If you are considering a swarm subwoofer system, do you have provisions for IC and power to those rear subs without wires across the floor?  Also, if your speaker wires must pass by a doorway or maybe a fireplace, now is the time to consider some sort of conduit(s) that can carry those wires under the threshold or through the fireplace and allow for future wire changes.
• Power - 
• When considering outlets, think about where your equipment will be located, i.e., will the electronics be on one wall and speakers on another?  Might you want monoblocks near your speakers, and therefore need power outlets near where speakers will be located and away from the other electronics?  Will you possibly have HT equipment that you want to locate and power separately.  
• When considering power, there are some here that buy into the viewpoint of having only one power line for everything and that solution works for them.  OTOH, I have had absolutely no noise issues whatsoever with multiple lines that are all run off the same side of the main electrical panel.  I run high powered amplifiers that each have their own 20A line.  I have a third 20A line for the electronics.  Nothing else is powered by those lines - the wires run directly from the main panel.   In addition to the audio circuits, have your electrician install his regular circuits for lighting and other normal household electronics.
• 20A circuits are probably most common for those who run dedicated lines.  Like many here, I upsized the in-wall wire for my 20A circuits to 10 awg size, which your electrician will tell you is only necessary for 30A circuits.  Some here use special "audiophile" wire and there are places that cryo treat romex, if that stuff is important to you.
• Consider your situation, and the location of your audio room relative to the main panel (although you indicated it would be close), and whether you might want to set up a sub-panel nearer to your listening room and have all the audio lines run directly from that - that would be a discussion with your electrician
  
• Some here have promoted the benefits of whole house surge protection that your electrician can install now and some use large filtration units for the audio related lines.  
• Do your stream music or have a server?  If a server, do you want that in the utility room? Do you need to route wires and power the server?
• Is this the lower level with a floor slab-on-grade, or a suspended floor on wooden joists.  If on joists, do you want additional blocking, reinforcing, subfloor thickness, or even deeper joists to reduce deflections, or maybe just reinforcement beneath where your (large?) speakers will be located, or below your turntable (if you have one).
• Some people have had good luck running fiber cables from their router to their digital audio equipment.  Now would be a good time to run fiber in addition to your LAN cable, if that is something you might consider using in the future.  I have both and don't really hear a difference yet but need to listen more.  Fiber cables are cheap so running one in addition to a CAT LAN cable would not cost a lot.  Consider which CAT series cable you want - there are threads here and other articles discussing pros and cons, which mostly have to do with different levels of shielding.

These are the main issues I can think of based on my new construction experience and the things I have had to do or wanted to do later.  I am sure others who have built rooms can add to it.

Below are some links you might find interesting wrt your proposed room.  
The electricity delivery articles offer similar recommendations with a few specific recommendations that vary somewhat between articles. 
To the question of one vs. two or more dedicated lines, most of the linked recommendations address multiple dedicated lines.  Michael Fremer from Stereophile recommends only one line to power the whole system to reduce the risk of ground loops but the linked articles do not necessarily support that recommendation.  IME, you shouldn't have ground loop issues if all the dedicated lines are of similar length and all terminate on the same side of the electrical panel.  My 3 dedicated, 20A lines are dead quiet.  You need to make that choice carefully as it would be hard to add new lines later.  You have one chance to easily construct and finish your room during the initial construction so I suggest looking at the articles, and considering the following when deciding how to wire the room;

• your system's physical layout and potential future changes (i.e., front end components on a side wall away from the amplifiers, monoblocks near the speakers, etc.), 
• power needs of your gear and particularly large power amplifiers (look at the  DTCD — Dynamic Transient Current Delivery thoughts in the Galen Carol article), and 
• whether you might want certain types of gear on a different circuit (i.e., in the event you want to use a conditioner on some gear but not all)

Definitely have the electrician run a different circuit (separate from the audio gear) for general use outlets for things like lights, televisions, where you plug in your computer, etc. Also, consider a whole house surge protector.  If the audio lines will be significantly different lengths, you may think about setting up a subpanel and then running only the audio lines from that but you can have that discussion with the electrician.  Links below:

• Improving your Listening Room Wiring – By Vince Galbo  
• Electrical Delivery Systems Overview - Galen Carol  
• Building a Sound Room: A Personal Journey - Jason Victor Serinus  
• How To Install A Dedicated AC Line - Paul McGowan