An easy way to mock up the situation to see what will work for you is to put the right number of rows of HO sectional track inside a cardboard box of the approximate height as your planned staging track access and try rerailing rolling stock on the various tracks. This should give you an idea of what dimensions might work well for you. Second the thought of rerailer track sections in your staging area. As long as Murphy is around, guess where your derailments will occcur?
my thoughts, your choices