Most major brand televisions will, or at least used to, list requirements for recessed in-wall mounting. That would include the space needed above, below, and on the sides of the television for proper ventilation.

As far as speakers, the center can be wall mounted just below the screen and the FL & FR mounted at ear level height to the left & right of the screen on the front wall. You may have to do some trial & error on insulation behind the speakers for best sound quality. You may also wish to purchase FL & FR speakers with an adjustable internal mount for the speakers themselves to optimize direction.

For the sub-woofer, a doghouse type opening often works better where the sub sits on the floor directly and eliminates vibrations and rattles in the wall.

The rears should mount about 2-3 feet above ear level on the back wall near the corners. Again, adjustable wall mount speakers are helpful here as well.

Remember 5.1 speaker placement is very directional and is meant to bring the proper imaging to the viewer as was intended in the audio mix of the movie.

Having your left and right speakers recessed or wall mounted will affect sound staging and the imaging.

Have the level of the tweeters at seated ear level (about 40" off of the floor).