The key is planning, planning, planning.
If all you want is some speakers in a bunch of rooms in the home, then think in stereo pairs. DO NOT USE ODD NUMBERS!
Speakers are sold as pairs, install them as pairs. There are some locations that use things like 'rock speakers' around a pool that may be appropriate for a single speaker in a lot of locations, in which case you will need to run those as mono instead of stereo at each location.
The main thing is to get a speaker wire at every speaker location.
Pick a head end (a central location) where all of your wiring will run back to. This location should afford you expansion as well as access. A small space in your family room is a TERRIBLE location! A unused closet or a storage/unfinished space in your basement is much better.
Be aware that surround sound receivers are not the same thing as whole-house audio solutions. In fact, they tend to be terrible at this functionality. If you want whole house audio, you should look for products and solutions designed around delivering a good experience.
Home Theater Direct has some whole house audio packages which include proper amplification as well as iPhone control for a reasonable price.
So, you also want to consider control. Whether you want everyone to be forced to use their phone to adjust volume up and down or if they want to be able to use a on-wall keypad to adjust things. I'm a big fan of having both available to anyone using the system. So, I have keypads, remotes, and a iPad available for whole house audio control as part of my setup. When my wife broke one of the remotes for our family room, she was able to use the iPad to start watching TV. It worked well, even though she didn't use that as the main control ever (like - ever!). Easy enough.
Yes, I've got a bit more of an extreme setup in my home than almost anyone will have, but I know this stuff backwards and forwards. There are 'cheap' solutions which you can do with just volume controls and a speaker selector and a single amp if you want to as well. Nothing wrong with that as a choice, but be sure that you understand the limitations you get when you do that. Same with using Sonos. Know the advantages and the limitations.
My system (I need a new thread on this)....
This past year I moved. My old home was pretty well setup, but didn't have any land and with young kids it was time for a new home a lot closer to my office. So, here I am, less than a mile from my office, with some land for the kids, but my old home A/V system left behind. You know what...
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