It would seem to me that the dynamics of opening a cafe inside an apartment complex is a very specific situation. In a sense, it is a micro-market which will have it's own market potential. Have you tried polling some of the tenants? Is there a disproportionate representation of people who, for religious or cultural reasons, abstain from coffee? How big is this "market"...and what are their current habits? Is there a convenient coffee house close-by that would represent an obstacle to you gaining the lion's share of business in a timely manner...ie before the lack of business forces you to close?