Wall Street will watch Costco’s (COST)  stock closely this week with the food and general merchandise retailer set to report its fiscal fourth quarter results on Thursday, September 26.Let’s see if it’s time to buy Costco’s stock as earnings approach and look at how the bulk scale retailer stacks up to some of its competitors such as Walmart (WMT)  and Amazon (AMZN) .   Costco’s Q4 Expectations                                          Like Walmart, Costco has strived to expand its digital growth to compete ...