I have done considerable research on this subject, and gratefully have been provided with the most thorough answer from a professional one could hope to get. I am posting it as follows in the event other GardenWeb users have similar questions...

"Wireless is a great way to move signals around without having to open up the walls, it can save a lot of patching and painting. If the walls are going to be open anyway, though, you'd be a fool not to run a wire to every place you think you might possibly someday want one, and then run some spares just to be sure.

Sonos is an excellent system that sounds like it'd be perfect for your immediate needs, but you should still wire it. Sonos boxes can communicate wirelessly, but if you plug each one directly into the house network you'll have much less noise interfering with your wifi and won't have to worry about placing each box so that is within range of another. Sonos units also require wiring to the speakers, and you might want those to be installed in the walls or ceilings and wired to wall plates (in each room or all in a central location.) If you think you might want installed speakers at some point, it's really easy to wire for them while the walls are open, then just sheetrock over them and leave them there until it's time to cut the speaker in.

For maximum flexibility I would recommend the following:

Figure out where your router and modem are going to live (let's say the basement, maybe behind the stairs) and mount a network and cable/satellite distribution box there. This should ideally be someplace accessible for when you inevitably need to reboot these things. To this box you should run the incoming lines from the street: cable, telephone if you're doing that, and also satellite (run a few RG-6 coax up to the roof or attic now even if you're not getting a dish right away.) You'll also need power, typically the box will have a knockout where your electrician can install a receptacle that you'll use to power your modem, router, switch etc.

This box will be the hub for your wiring system, all the rooms will be wired directly back to it ("home run" in wiring-speak.)

To cover the house with good wifi signal, you should pick places for wireless access points and run a CAT6 to each of these locations. For a 2500 square foot single-level house I would start with 3 access points, with one in the middle and two more out toward the ends. They should be someplace where you can unobtrusively mount them high on a wall, and where you can get to them for rebooting as needed (hall or bedroom closets are good for this, as are high shelves in built-in bookcases) They will typically need an outlet for power, so plan for that too. I highly recommend getting the access points and setting them up before the walls are closed, so that you can test whether the coverage is adequate and change locations or add more access points as needed. At least bring one and try it in each spot in turn to get a ballpark idea of coverage.

For every large room in the house (bedroom, office, kitchen, etc.) you should have at least one CAT6 drop for a network jack. If you're feeling flush, make it two per location; CAT6 is primarily used for network, but it's cheap and can be used for landline telephone or repurposed to do almost anything else. These should go back to the main box where you will install a network switch, which could be big enough to make all the jacks in the house active at once, or you could get away with having a small switch and plugging in only those jacks that you're actively using. With this setup a housemate/tenant could conceivably have their own second modem in the box providing private internet service to their portion of the house.

For any location where you might want to put a TV, I would run a bundle or a structured cable ("structured cable" is just several standard cables wrapped in an outer sleeve that makes it easier to deal with) containing 2 CAT6 and 2 coax cables. This gives you a lot of flexibility as far as hooking up cable or sat boxes, internet-enabled set-top devices, etc. This bundle should go from the spot in the room where you want the equipment for the TV to the box in the basement. You should also add a conduit or "smurf tube" from the equipment location in the room to the place where a wall-mounted TV would actually hang. This will allow you to pull one or more HDMI (or network, or Kinect, or whatever crazy gizmo comes next) from the equipment up to the screen without draping cables down the wall. Also, of course, consider power requirements for the TV and have a recessed "clock receptacle" installed at each TV location. Just stapling a long HDMI cable inside the wall is a bad idea, since HDMI ends can't really be replaced in situ so you'd be out of luck if the cable were ever damaged, to say nothing of potential future standards that might use different cables or connectors.

For any room where you might want sound, you should pick speaker locations on the walls or ceiling (ideally with good separation but not too close to a corner, and not opposite one another such that they're faced directly at each other) and from those spots run speaker cable first to a spot in the room where you might want to put a stand-alone audio system or Sonos box (this spot should also have network and power) then from there back to the box in the basement. This will give you maximum flexibility when deciding whether you want a centralized audio distribution system or a bunch of little independent systems. I'd recommend 16 gauge wire or thicker, brand is honestly not so important. You can use a single 4-conductor cable so you just need to run one to each room and split it where you need it to reach both speakers, simplifying the wiring process and making it easier to organize the cabling at the main box.

To run the music system, one cheap and expandable way to go would to get a single Sonos Connect box and hook it up to an amplifier, then run the output of the amp through a speaker selector (I've never used this one but it would let you drive 5 sets of speakers from a single Sonos/amp combo. It won't get very loud but is the cheapest way to get started.) You can then set the relative volumes of your zones on the front of the selector and use the Sonos app on your phone or computer to adjust overall volume as you listen. You can easily expand this system as needed by adding additional Sonos units and amps and decoupling them from the selector, or add more zones by splitting the output of the Sonos and feeding it into a second amp/selector combo. Sonos does a good job of combining units to play in unison for when you want the same music everywhere, or you can use multiple units to listen to different things in different rooms. This approach allows you to keep all the amps and equipment in a single location, so you can have sound without devoting shelf space in the room to it. It'll also help you save costs on power conditioning, since you only need one big surge protector.

Here are some guidelines for making sure the work is being done competently and that the right materials are being used:

A good home network specialist will test each network jack and not consider the job done until they all test good. An electician will usually not have the tools to do this as they wire, but they'll be cheaper and it might be worth the savings to you if you can do some basic testing yourself: plug in a router at the main box and then walk around with a computer and making sure it can connect to the router through each jack, then call them back to fix any bad ports. Either way, you should make sure the jacks are tested before a tenant moves in.

All your network cabling should be punched down into a patch panel which should be clearly labeled with the location of each jack. You can then use short ethernet cables to connect each jack to your network switch.

Wireless access points should be set to use the same ssid (network name) and password scheme but different channels. This will allow your phones and laptops to seamlessly roam from one access point to the next as you move around the house.

Coax should be quad-shield RG-6, sometimes people try to cheap out and use RG-59 which is really not adequate for long runs

Low voltage cabling like speaker and network should not be bundled with electrical wiring or run parallel with it within a foot or so for long distances, this can cause noise and interference. Whenever possible low voltage cabling should cross electrical wiring at a right angle.

Standard landline telephone should never share a CAT6 cable with network. (It's actually possible to wire this in a way that will seem to work fine, but your network's speed will be severely degraded because your equipment will be forced to use the older, slower 100 megabit standard rather than the current gigabit standard.) This is different from VOIP that uses the network itself to digitize the telephone signal a la Skype or phone service through your cable or fiber ISP, I'm talking about physically wiring an old-fashioned phone jack to two conductors of the CAT6 that you're also using for network.

A switch is required to "split" the network connection, and an electrician who tries to split ethernet by just splicing (or "bussing") the wires together is bulshitting you and has probably never wired ethernet before, because it won't work at all. I shouldn't even have to mention this but I've seen it done more than once. It's not so bad if they home run it and just splice it all together in the box like it was telephone (you can just rip out their bussing block and replace it with the right stuff,) but if they try to daisy-chain more than one jack it's a nightmare.

On more note; any crawl spaces should be connected together by as much conduit as you can squeeze in, ideally 3 or 4 2 inch pipes, so that there is a path for future wiring to take from one end of the house to the other. They should be clearly labeled at each end so that future workers can find them and know where they go even if you've sold the house or forgotten about them."