I would limit the group to only the Senior Leadership Team.
If you've created the Accountability Chart the right way - structure first and people second - then you should have each major function represented at the senior level.
At the core of EOS is the idea the we need to create vulnerability based trust. This trust leads to healthy conflict, which in turns leads to commitment, which leads to accountability then to results.
Establishing this type of trust is easier in smaller groups and is critical to ensuring that all of the right information comes to the surface.
Lastly, EOS is a system for creating alignment, but not by consensus.
Hope this helps!