In terms of facilities you're only really looking at how quickly you can safely get supporters in and out of the ground. Once supporters are in their seats there's going to be very little difference between a brand new PL stadium and an old League 2 stadium - give or take you'll have fairly similar percentages of capacity that can be used. You'd hope, given what's at stake, that the EFL could quickly put together a group that assess each stadium and calculate how many supporters per x minutes enter each stadium and work from there.
edit: I guess you've also got things like toilets etc, although I guess that could be linked to capacity too. Who knows.
edit: I guess you've also got things like toilets etc, although I guess that could be linked to capacity too. Who knows.