Congratulations on the finishing project. They're quite a lot of fun, including the various wrinkles that accompany a construction project. We completed a similar basement finishing project in 2015, including our own theater. I kept a construction journal from design through completion if you're interested -- link at bottom.
Based on the layout shown, it looks like there's a pocket door on the right, correct? Meaning in-wall side surrounds might not be an option.
General thoughts:
- With walls open you can run wire and conduit easily to set yourself up for a phased deployment (5.2 -> 7.2 and beyond)
- Think about whether you will go on-wall, in-wall (depending on design constraints like the doors/windows) or mix-n-match
- Location of subwoofer(s). You want to have several options to try out, to determine the optimal location for the space
- Sounds like Atmos is in your plan with 5.2.4 so check your ceiling layout for placement of the overhead speakers
For my space, which is similar in size to yours, I started out with Atmos support as a design objective. Going into it, I was fairly sure it would work out, but I ended up making adjustments as the project developed.
In the end, we got a 9.1.2 Atmos system that could expand to 9.1.4 or 9.2.4 fairly easily.
http://havingfunalongtheway.com/basement-home-theater-design-construction-series/
Good luck with your project.