How were you planning to configure the height speakers? ATMOS or side height for Auro 3D? The issue is having the rear surrounds in the ceiling. For ATMOS, you need your 5.x.x bed layer at ear level. If you move the rear/surround speakers into the ceiling, then it is not recommended to use any ATMOS speakers. Just go 5.0.2. It is not ideal but will add some surround effects for movies.
For proper ATMOS, you need to have the rear/surround speakers at ear level, so some small book shelf speakers on stands at the corners of the sectional. If you can fit those, then the room is big enough for 4 ATMOS speakers in the ceiling (or surface mounted angled height speakers) for 5.4.2. For the bookshelves, I recently purchased a pair of
True Mini Monitors from Philharmonic Audio ($380 US) which perform very well for their size. Then it's a matter of whether you can go in-ceiling or not, but with the ceiling speakers try and get speakers with an angled baffle which point at the main seating area as that improves the frequency response in the listening window. If your AVR only supports up to 5.2.2 then I would install the ceiling speakers slightly ahead of the main seating area. They look too far forward in the diagram. This also depends on the ceiling height so you need to refer to the Dolby ATMOS specs for proper installation angles.
Here's a link to the PDF.