What are you intending to use each of the screens for???
Define the mission first, then design the panel to fit that.
I have never used either a Skyview, or a 696, so I am speaking from a position of ignorance , but here is my dos centavos.
The Skyview has a nice mapping feature, as I recall, and they are working on improving it.
I question the need for the 696??? Removing it will pay for the 10" Skyviews.
As to the layout, place the most used screen directly in front of you, and the next most used screen next to it------considering you can choose what is being displayed on the Skyviews, this will become a configuration issue, not a hardware mounting issue.
As to the radio stack, install full length vertical mounting rails now, cut the opening in the panel now, and install a cover plate there until you actually do the upgrade. Then it will be only a matter of removing the cover plate, positioning the tray, and drilling the mounting holes in the existing rails. A little extra effort now will save time and work later.