A very incomplete answer, based on personal experience: Do
not separate varieties throughout the orchard. Each cultivar ripens at a different time, and chasing all around the orchard to find, and pick all the Belle de Boskoops together is no fun. You will have quite enough difficulty keeping track of where the Boskoops are in the first place without trying to search through the entire orchard for each instance. It becomes more problematic deciding what to do when one of the Boskoop trees in the middle of the block dies, and you set about replacing it with a new cultivar - too many such random replacements and you end up with chaos again. (I got some scion wood from a very old, local Seek No Further tree last year. This is now successfully grafted onto rootstocks at opposite corners of the orchard, because there happened to be gaps in the rows at that time.)
Broomholm OrchardZone 5b in Nova Scotia