I can not imagine any advantage to have all the residences in the same xxx.pln unless of course you would like to have them available for a little bit of editing in each of them.
If all the residences are the same, it is almost required "hot link" method so that you do the editing in only one file and it gets updated in all the instances placed in the site drawing.
Even if the residences are different, depending on your machine capacity, you can have Archicad opened in more than one instance. For example: one AC is opened with the site, another AC is opened for building A, another for building B, and switch windows back and forth saving the residences plan and updating the links in the site plan.
For organizational purposes, try to have the same set of Attributes for each residence file.
Hope this helps
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