While not my recommendation as opposed to traditional speakers, if that is your only choice, it can still work well.

Center channel should be in line with the TV and as close to the screen height as possible.

Front surrounds should be at about ear height and form about a 45 degree angle with the seating position (22-23 degrees to each side of the line to the center speaker. Spacing is dictated by your viewing distance to maintain the angle.

Rear surrounds can either at 90 degrees to the seating area (each side of the seating area) or behind the area. If behind, they should be at about a 60 degree angle to the seating area. Placing the speakers fairly high in the side walls firing at each other is probably a better option than firing straight down from the ceiling. When you set up your receiver, you will set it for these speaker positions and heights.

The sub can go virtually anywhere.

The problem with in wall speakers is that you can not adjust the position for better sound like you can with regular speakers. You are pretty much stuck with your first, best guess. You also have a much narrower choice of quality levels.