This is a complicated answer just because there's so many options and variables. We always tell people to run more wire than they think they'll need.

Proper speaker wire is fire rated for in-wall use - don't run lamp cord in your walls. 18 gauge, two pair or four pair is typical. While the walls are open; run at least one Cat6 to TVs, potential wifi access point locations, security camera locations, door bell, light switches, even speaker locations and someplace you think you might want a source component (turntable, etc). If you want controlled shades, they may take special wiring which you'd definitely want to run now. Worse case, 18/4 and Cat6. Everything should start from a central location not far from your electric panel.

You'll need to balance how you want to control the system with how the system you want can be controlled. If you want in wall keypads or touch screens, that control system needs to be compatible or made compatible with your source gear. If you want to control everything with an iPhone or iPad, you'll need to look into a control system that's compatible with that.

Consider that a ubiquitous 110v commercial amplifier can likely power all the speakers in your home but it lacks volume control. Most whole home amplifiers lack a volume control you can operate from a mobile device. There are in-wall volume controls that can sit between the amplifier and the speakers. To use those, you could run 18/4 (and maybe Cat6) from the amp to the volume control then 18/2 from the volume control to the speaker. You could also consider a matrix switcher with preamp. This would distribute one or more sources to the amplifier channel (speaker zone) you choose and possibly give you remote volume control.

Those are just some thoughts. You might want to check out these sites for equipment ideas: monoprice, sweetwater, snapav, russound.