LCA ZWC

Hi all, I am currently doing research on the hygiene of a reusable cup. In this research, I am contaminating the cup with coffee+milk+sugar and chocolate milk. Then the cups will be tested under different variables like different storage times, 1 time used versus multiple time used cups and also comparisons between conventional alternatives will be made. after contamination, the cups will be washed in a professional dishwasher and examined organoleptically. Then the cups will be swabbed and the swabs sent to an external certified microbiological lab. They will test the cups for : -CFU/cm2 -enumeration of Enterobacteriaceae My questions are : - how much cups should I test per variable to get a statistically reliable result? (i have spoken to labs and they say n=5 should be sufficient but this is normally done for process controls so periodical testing, and not for self-contained researches like this). -would you suggest testing for CFU/cm2 and Enterobacteriaceae is sufficient to draw conclusions about the hygiene? - Could chocolate milk be considered a worst case scenario? ( considering its neutral PH high nutritional value and stickyness?) Thanks in advance!