The number of passages you should expect during expansion will be cell type dependent particularly when working with primary airway epithelial cells. If you are using commercially available cells, the vendor will typically provide the maximum number of expected population doublings. For example, Lonza guarantees their cryopreserved human airway epithelial cells through 15 population doublings. You will need to find a balance between the minimum number of cell passages required to create a working cell stock and not reaching the cell population doubling limit prior to permeable support seeding. For studies involving testing many conditions, using a smaller permeable support format such as Corning HTS Transwell-96 permeable supports can help in minimizing the number of cells needed for your study.