I own an alarm company and we also do non audiophile whole house audio and surround sound systems. Typical rules follow regarding a triangle between the speakers and your listening space. If you haven't put up sheetrock yet I suggest you get preconstruction rings and have the sheet rock guys rotozip the holes for you. This is much easier than cutting them later especially with the blown in insulation.
Also something to think about is how high your speakers will be mounted, the higher off the ground the wider the area they will cover. Just remember when they are mounted on the ceiling the tweeter is basically pointing at the floor, of course with an angled ceiling that improves a bit.
We pretty much just do round in ceiling speakers and not in wall. I don't suggest using rectangle in wall speakers as they don't look as nice and in order to get them at ear level you take up your picture walls
We use Proficient (proficientaudio.com) as they are pretty good for back ground music, have a large selection and are a good value for the money. You have many to choose from, Kef and Klipsch just to name a couple.
If you have more questions feel free to PM me, I'm happy to help if I can.
Greg