sirhc80
2
One scanning system is sufficient, but you are free to build more… 
But wth you need 20 bays? 
Here you find, how many bays per stand are needed…
I recommend to look at some tutorials or airport designs, before building up huge baggage systems.
As I did myself, many people massivly overdo with their first setup, as ingame-tutorial is not yet perfect…
This thread is imho very good, there can be found videos, too: