In my experience, the thing most likely to cause a problem is going to be the building's management - whether its an apartment, condo, or co-op. With a 2 or 3 low profile people you'll be ok, but good luck trying to get away with actual employees coming in and out all day.
6 people in an apartment sized for 4 may be a nuisance.
"Commercial" activity generally refers to customer traffic, not personal work.