Yamaha - 8" 3-Way In-Ceiling Speakers (Pair) - White

No reason why not...providing that you mean 2 of them and not 6. I believe the model that you have mentioned is a stereo unit. I have an Onkyo 5030 or whatever 2 channel hooked up to a pair being used in series with a second zone amplifier to do multiple rooms.

yes they will

yes they do

You definitely want a center speaker, as it will allow you to hear the voices and talking clearer and at a good volume, and still hear your front and rear speakers, without having to turn the volume up louder to hear everything as well. They don't have to be any certain distance apart, but assuming your front speakers are approximately 12 feet apart or so, just center the speaker between them, maybe 6 feet apart. Center speaker makes all the difference, and you may want to get a sub woofer, to give you the feel of being in the movie with the base effects

The size of your rooms you want speakers in should determine how many you prewire for. Most speakers are mono, designed to work in pairs for stereo or in multiples for surround sound. There are single speakers that have dual voice coils meant to be used as a stereo speaker. They will require 2 sets of speaker wire ran to the speaker. I would recommend that in larger rooms, like bedrooms, office, or kitchen, that you should prewire the home for a pair of speakers to be used in stereo. It will provide the best sound. Be careful to consider furniture placement as well as in ceiling obstructions when doing the prewire. (I.e. Don't prewire your master bedroom with one speaker above the head of the bed and another at the foot. Like wise, don't prewire where your HVAC, plumbing, or even roof rafters will limit what kind of speaker, if any, can be installed in the ceiling). In the bathrooms I would wire for a single stereo speaker. 2 speakers tend to play against each other in small spaces and muddle the sound. Music is recorded in stereo (or better) so you shouldn't ever think of prewiring for less than stereo.