Just generally. 14 gauge is a bit thin for long runs. Id probably run 12 gauge for runs over 35 feet or so. And yes, you must consider your local building codes. One speaker,/ channel per pair of wires (+ and -). For stereo, obviously two runs of wire are required . One speaker equals mono output. You do know that each amplifier in a receiver handles only the left or right sound signals, not all of them, unless the whole amp itself,or the source is monaural, right? Some may have a mono only selection, but these days , very few. The wire is not a convenience, each set (+/-) carries the signal from a particular amplifier channel. Consider in-wall rheostats to adjust volume locally, if
you are in a new construction situation especially, since later threading wire through finished walls is a pain, but simple pre-finish work. know well ahead of time what type of system you intend... it either needs to end up an eight ohm load at the receiver, or be set to run only one pair at a time, or be a 70 volt PA system. or such ..unless blowing out amps is not an issue for you. Im not passionate about permanent in-wall installations save for intercoms or large open area store and business use. People tend to move furniture around, redecorate, upgrade speakers, so on. most speakers are free standing for a reason, so they can be moved around to take advantage of the room for best imaging, and to place them at ear level. Most ceiling speakers do not provide real stereo imaging when shoved into ceilings - you end up with Elevator Muzak not music.reproduction. Its good for background noise, like in a restaurant, not theater or critical listening. Be sure to keep a good schematic of where you run what, and label everything, is all I can say.