AE can handle anything up to 16000x16000 pixels. For the matter at hand it's irrelevant most likely, anyway. At most this will probably be normal 4k output, or 3 or 4 HD streams split and played back via synchronized devices. Either way, the actual physical layout of the panels will not be mapped 1:1 because: Why should anyone? That's the same thing like when in print large format posters are printed at effectively 15 DPI at times. You know, viewing distance vs. dot size vs. perceived visual density. You really need to inquire/figure out what exact resolution is required and how you are supposed to deliver it because otherwise you might end up with a 12k output or something liek that for which no playback device exists. That also will take care of your insane amounts of data and render times - they simply will never be necessary.
> AE can handle anything up to 16000x16000 pixels.
The maximum pixel dimensions for a composition are 30,000x30,000.
Thanks for all the details about the screens, but that stuff is pretty irrelevant and dpi is absolutely useless. Here's why:
You can play a 1280x720 video from Vimeo on your phone. How big is that screen? What would be the dpi on it?
You can play that very same 1280x720 video on your 72-inch HD TV set. NOW what's the dpi?
You say, "It's still 1280x720".... and you're RIGHT! It's the playback device that has the greatest bearing on what you'd do in AE. So you have to find that out before we can get you useful advice.